Simple question

I have several EAs that i compile with no errors. The EAs show in the navigator, but when i double click them or drag and drop them to a windows NOTHING happens at all.. No error message etc.

Some EAs i have (id say about 50%) work fine and i get the x or the sad face or the smiley face etc. Other EAs do absolutely nothing.

I obtain the EAs of threads in forums that in some cases have thousands of users with no problems. Ive googled for a solution to this and tried to check im no doing anything wrong, ive even uninstalled and re-installed meta trader..

any ideas? There doesnt seem to be a pattern.. For example the 'Framework' EA works fine, and i have a MACD EA that works fine, but things like the cowabunga EA (from babypips), the C4 EA for exmaple wont work for me. They are all popualr well used EAs.

(Vista 64, Intel E8400, 4 gig ram, 8800Gt, loads of storage, latest version of MT4, ive not tried beta testing MT5 or anything silly that may have left residual files)

Any suggestions greatly appreciated.