|See event viewer logs and maybe dump files. See also perfmon for memory leaks or other fails.|
Run memtest or other diag suite.
I used to do debug for a computer maker for a while some time back. You would be suprised how fragile a system is. Most times major issues would be found on OS changes or OS versions. For example, a motherboard would work for years on a version of an OS. The next OS or even updates would cause the board to fail. Most times a firmware chip or clock change fixed the issue. Sometimes we had to add or delete parts and connections to get it working. This may have affected hundreds or thousands of boards. Sometimes it was a component that may have passed for that OS, just didn't work for the next OS.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10