If this started out of the clear blue I'm still leaning toward malware, but we can try a few things.
First, go to the websites of your video card, sound card, and (if appropriate) ethernet card manufacturers and download and install the latest drivers. Also check for a bios flash.
Then boot to the recovery console and run chkdsk /r
If the problem persists, let's try a selective startup:
Open msconfig and on the General tab choose "selective startup" (uncheck all three items) and reboot. Does the problem still occur? If not, start adding items back to msconfig one or two at a time, rebooting after each change, until the problem reappears and you'll have identified the offending process. This is clearly a time consuming procedure, but it is the best way to determine if some process loading with the system is the cause of your problem.
After you've isolated the cause, do not use msconfig to permanently disable the process. Instead, if it is a service go to START - RUN and type: services.msc (then press enter) and disable the service OR, if it a program, you can download & run a simple app such as Mike Lin's Startup Control Panel (http://www.mlin.net/StartupCPL.shtml
) to enable, disable, or otherwise manage startup programs.