3.3 Won't run on my WinXp machine

I have just installed 3.2 and then 3.3 on WinXP, and for some reason it won't run. My hard drive just rattles on endlessly as if some file is missing or something.

I have gone through the usual checklist of updates and drivers, uninstalls and cleanups to no avail.

When I click the shortcut, I get a quick hourglass icon, my harddrive starts reading as it normaly would, and then continues like that infinitely. I can't even abort from the taskmanager.

It does not seem to be the harddrive, I have everything else running smoothly (and version 2.6 ran just fine).

Does anyone have a similar problem or preferably a fix to it?

 

Fixed! Thanks to this checklist.

I manually updated .net and set my AV to ignore unity.exe