Bah, apparently I can't read then.
You can use this http://www.technibble.com/repair-tool-of-the-week-memtest86/ to test for bad ram, and this http://support.microsoft.com/kb/929833 will walk you through how to use SFC to check for corrupted windows files.
Without error codes etc these are basically guesses, but they're easy to check and eliminate as problems. If it's not bad ram, chances are it's power supply or temperature related. Odd that temp would be a problem when it's in standby mod, but ram probably shouldn't be an issue in that case either (if it's going into standby happily anyway).
Just for the sake of completion, scan for viruses/spyware too. It's unlikely they're the culprit, but sometimes they cause more complication than you would think.