Unable to download apps on Mac App Store

I have a mid 2011 MacBook Pro running Moutain Lion 10.8.3.

Since yesterday I've been unable to download any apps on my App Store.

I've searched forums and websites here in Brazil and abroad to check if it was a Apple's problems but found nothing.

Checking here in Community I've found some tips, so I've already done as follows (not necessarily in this order):

1. Logged out and logged in my Apple ID (I can access my Apple ID normally);
2. Checked if there was any other apps on download list;
3. Searched for any apps without "receitp" using "mdfind kMDItemAppStoreHasReceipt=1" on Terminal;
4. Removed my BOOTCAMP partition;
5. Re-installed last ML update (10.8.3);
6. Removed any cracked aplications;
7. Re-idexed my HD with Spotlight.

I'm almost formatting it, but I don't have a instalation disc nor a updated backup, so I figured I should try seek any help here.

Thanks in advance and sorry for any mistakes, I'm not a native speaker.