[Nuslos]

Has happened twice now, once in the middle of a game, again trying to surf the web.

Also got a notification bubble saying that C:\WINDOWS\System32 was unreadable or corrupt, to run chkdsk to check for errors, nothing wrong there..

[bacchus]

Try running some spyware / adware software and some registry repair apps. The joy of dealing with windows.

[Tomchu]

In 99% of cases, IRQL_NOT_LESS_OR_EQUAL is caused by either bad RAM or a bad driver -- usually video or sound.

Though in your case it could be the hard drive, too. I've never seen such a notification bubble in all my years of using Windows.

[seanc]

I've only ever had that bubble when my external drive started playing up, make sure you have backups. What apps. are you running when it BSODs?

Tomchu is right, it usually is sound or video, in my case it was sound, not sure if a driver update fixed it or not but it doesn't hurt to try.
If you check the Event Log, which can be found in Start|Settings|Control Panel|Administrative Tools| Event Viewer and look at Application, see if there's an error entry for the time when the computer rebooted, it may help you to track down the issue.

Another thing we can do is to read the crash dump files that Windows (should) creates, to do this we'll need to download the debugging tools package for Windows and then use Windbg to open the .dmp file. In this file it should say

Probably caused by xyz.sys