Various annoying system issues

Right, I've been re-directed here from the malware forum, as having examined my logs, apparently, my computer is clean.

My problems started about a week ago - Firefox would refuse to find some websites intermittently. Gmail and livejournal would seemingly flit in and out of existence - also, my desktop Gmail notifier also struggled to find Gmail. Next, icons started disappearing off my computer, and my wallpaper turned black.

I decided to do a (long overdue) formatting, and I re-installed Vista (32).
The Gmail problem seems to be fixed, but all the icons for my pictures have disappeared again, and my wallpaper is black.

Oddly, if I select an image on the web, and select "make desktop background", it works fine, but if I use an image on my computer, no dice.

I don't know if this is helpful, but a list of the software I've installed since my formatting:

Firefox 3
iTunes
Norton Internet Security
Ccleaner
Spybot
Malwarebytes
Combofix
VLC Media Player
Skype
Mega Manager
Imgburn
WinRAR
Gmail Notifier

Is this a known problem? If so, are there any solutions?