Help please.

CONTACT SUPPORT FOR ASSISTANCE..
we're not the support, i think.. :D

Did you try using a coupon? coupons won't stack and give you this error.

Try reinstalling steam:

• Go to your steam folder, delete everything except Steam.exe and the folder "Steamapps" (this is where all your downloaded games go, that's why you don't delete it)
• Run Steam.exe again; it will reinstall steam and thus clear your cookies on steam, which might solve the problem here.

I once had a similar issue where somehow, during the halloween sale - the region of my store was set to US, so I couldn't buy anything either! Clearing your cookies should fix the issue (if it's this).

Maybe the servers are just over loaded atm? :o

Now i have error : "The current payment method does not match the country of the store. The cart has been converted and the updated total will show on the next page. You may also review your cart here, or change your payment method below."

That feel when you realize that steam uses IE's browser settings.

DESU DESU DESU DESU DESU

Only Steam support can help you with these kind of problems.

That's a very common problem for people who opens their steam accounts under a different ip which means you probably opened your steam account in a different country, or city, or ISP. Of course it will only take action when you purchase a game, so, only steam support can solve this and man that will be hard!