I experienced the IRQL_NOT_LESS_OR_EQUAL error on one of my older PCs, and it was due to bad RAM.
Download Memtest86 and run it overnight, see if it produces errors. If so, RMA/replace the RAM. If no errors are found or your system restarts or locks or something, then I'd investigate a possible bad PSU or motherboard.
But definitely check the RAM first. It's the easiest to troubleshoot and probably more common of a problem.
Edit: And if you're using cheap generic RAM, do so no longer. Always buy something with a lifetime warranty (Corsair, Crucial, Kingston, Mushkin, so on. I'm partial to Corsair at the moment) because if you ever have a stick go bad, you can mail it back to them for about 75 cents USPS first class and they'll send you a brand new stick immediately.