What should I do?

dont open it, wait for new pc. while you wait disable all "makeup" on your laptop

maybe give it to someone who knows what he's doing to clean/fix your laptop?

Use some lightweight OS, like Crunchbang.

You ever hear the saying: "If you want something done right, do it yourself"? I've worked on quite a few laptops for friends and family. Laptops aren't like desktops though, and I wouldn't attempt to take it apart unless you can find a service manual giving you the proper steps to open it up. They are like puzzles, and everything must be done in a specific order or you can break things. It's understandable if you're not comfortable doing it, but getting your hands dirty and doing it yourself is the best way to learn.

That said, dust alone won't slow down your system. If you have pets, then pet hair can get get tangled up in the fan, and if the fan slows down or stop, the CPU will throttle down to keep cool. Most laptops I've worked on have filters to prevent things like lint and fur from getting sucked in, and you generally would hear if your fan is not working properly.

Your problem might have too much "crapware" or "bloatware" running and taking up resources. Most laptops bundle a bunch of crap on them that startup with the system and try to auto-update themselves. You can attempt to remove these yourself. PC Decrapifier can help, as will CCleaner. Windows also has a built in tool that shows you what items and services are starting at boot. Click the start button and type msconfig.

Start with PC Decrapifier and uninstall anything you don't need or want.

Then run msconfig. On the Services tab, check the box to hide all Microsoft services, then sort by the Status column. Look at any running service and determine if you need it or not. Don't disable it here though, it's best to disable it from the Windows Services manager. To get that, click start, type services, and the one you're looking for is simply called Services (it should have an icon that looks like two gears). Find the service and if it's set to automatic, put it in manual and stop it. Services in manual can be called on to start when needed (and sometimes stop when they're no longer needed). If the service is already in manual and running, and you know that it isn't something you need or want running, stop it first, then set it to disabled.

Now go to the startup tab in msconfig. Once again, determine what you don't need, but this time it's safe to uncheck it here to disable it from starting up. To determine what services and startup items do and if they are needed or not, consult this guide.

Finish off by running CCleaner. Run the Cleaner part first, then do the registry cleaner. Don't just blindly run the cleaner with everything checked though or you could end up deleting something you need. Read the description of what each removes and decided if you want it removed or not. The registry cleaner is safe to run with everything checked though.

The best fix though is to do a clean install of Windows, not a system restore from the disks that came with your laptop as that will just re-install the crapware. Windows 7 images can legally be downloaded from Microsoft here. Windows 8 is a little more difficult. You will need your Windows 8 or 8.1 product key, and follow this guide. Either burn the image to a DVD, or look up a guide for creating a bootable USB stick. Install Windows and enjoy your crapware/bloatware free system. Before you reinstall Windows, make sure you download any device drivers and have them backed up to a USB drive first. If Windows doesn't contain generic drivers for your network card, you won't be able to get online to get them.

If you still think it's a fan or cooling problem, there are free programs to check this. Go here http://www.cpuid.com/softwares.html and download HWMonitor and CPU-Z. You will need to look up what CPU you have and find out it's max temp and core speed. The CPU slows down when not under heavy use, so you need something to put load on the system. I use Prime95.

Now that you have the above software, start up CPU-Z and HWMonitor. In HWMonitor keep an eye on the System and CPU temps, and in CPU-Z, keep it on the CPU tab and watch the Core Speeed under where it says Clocks (Core #0). Fire up Prime95 and run the blend test or the one that says it generates max heat. Let it run for a while, keeping an eye on the temps and core speed. You want to make sure your core speed stays at its highest rated speed and the temp. doesn't exceed its max. rated temp. If supported, HWMonitor will also display the fan speeds in your system. Finding the fan speed rating for your laptop might not be possible, but just watch and make sure the fan speed stays constant. If the CPU or system temps go to high and you see your core speed drop (and/or your fan speeds don't stay consistent), then you probably do have a cooling problem.

I opened my laptop, erm, 6 or 7 times already. Now there are a few screws missing their places but nothing's broken. Your friend's brother may have a loose keyboard connection, or he broke something in the process. Normally you can't break things much, unless you are really careless.

Service manual.

As long as you follow the guidelines listed here, and make sure to only do specifically what the steps list and do the opposite of what you do to take it apart when you put it back together, remembering to plug in what you unplug and stuff like that, you should be fine. Laptops are designed to come apart, they just don't always look like it. I've opened up dozens of laptops for my old job, and while it was intimidating at first, as long as you try to understand what each part is and why it's there it's easy. If you're just accessing the fan, it's easy peasy. Otherwise, you could try blasting compressed air into the fan and letting dust blow out; I did that once and saw a 20 degree improvement in temperature and a significant frame rate improvement.

your friend is noob i oppened 20 lap top last week and the only thing you need is a bowl to hold the screw a good memory to remember how to replace everything and the good tool to open it, the hardest part it to remove the key baord panel and the front panet because they are cliped instead od screw.

if you dontwant to open it, get a aire blower to suck the fan hole when the comp is running.

Hmm... Yourcat suggested air blower. Would cleaning the fan with a hoover without opening my laptop be good idea? :)