Vista - Unable to Download Anything

Hello, i have a laptop ~ 5 months old that I use almost entirely for the
internet.

About 3 weeks ago, using IE, I noticed web pages stared loading poorly, with
many errors. Photos would only half load. The problem got progressively
worse. Now, I am unable to download any new files...windows update, firefox,
spyware detectors, anything. They download ok, but when I try to install I
get errors saying the file is corrupted.

I ran norton antivirus full system scan with no adverse results.

I ran a memory test, with no adverse results.

I restored the pc to a point about 6 weeks ago, the problem persists.

I finally restored the pc to the factory default settings, the problem still
persists.

Any ideas?
I