I can't download anything what could the problem be?

You have to give more information than that, before someone can help you.

Are you able to connect to the internet and serf the net?

Are you trying to download updates?

Music?

Movies?

Got to give more specifics

It could be a virus and/or spyware. Download the following from a working computer, put itonto a cd, then install on your computer. Update it if youcan, then run a scan.

I would suggest downloading Malwarebytes Anti-Malware 1.37 from:

Malwarebytes Anti-Malware - Free software downloads and software reviews - CNET Download.com