YayMii said:
EDIT2: This just popped up in my Windows Update:
http://support.microsoft.com/kb/2505438 Could this be the cause of my problems?
Nah i don't think so, thats for slow performance, not "no" performance lol.
Complete freezing is still likely caused by a driver failing, could be a sound driver. the freezing could be a sign that the PC is waiting on somthing (a driver has suddenly stopped responding). normally in these scenarios, if you leave it frozen for 2 minutes, a blue-screen will occur, the PC will restart, and windows will have an error log to report. sometimes when you report these error logs, windows will have a solution.
unfortunately, you say it only does it after several hours. does the PC's performance change over time? like, does it get slower?
if it really did begin after installing SP1, i suggest reinstalling Windows 7, and then reinstalling SP1 as soon as that's complete (Before driver install).
you can use "Windows Easy Transfer" to keep your settings, and back up all your files to some other location.
if you can't or don't want to reinstall Windows 7, then continue debugging i guess
Have you ran Chkdsk or sigverif?
chkdsk Will scan your HDD for damages
sigverif will check your system files for valid signatures
sigverif may report a few files to you, such as drivers, this is normal, not all drivers are signed, especially with older hardware. Though if a newer piece of hardware shows, you may want to consider reinstalling whatever device it belongs to.
if you do have a bunch of files showing up beyond drivers,
you may be able to repair your system using the "SFC /scannow" command.
Just more ideas, hard to help when the problem can't be reproduced.