|Evaluate, troubleshoot, don't just assume and replace parts that might just be good still.|
Install Speedfan or similar to monitor your internal temperatures. Post back results, especially if hot.
Run Memtest86 via bootable CD to test your memory for errors. retest with one stick of RAM at a time if you get any errors. Replace as needed.
Run hard drive utility from hard drive mfg's website to evaluate your hard drive (also via bootable CD)
Oops. Just saw your temps posted, sorry. If those are typical, it is probably not a thermal issue.
Check your memory and hard drive, if they both come out clean, suspect the power you are plugged into as the problem (cannot be software related if it happens both on and asleep). Get a small plug in power tester that will show you through colored LED's if you have a ground fault or other power issues, if not then consider using a UPS to cover small power fluctuations that can cause the problem.
You have to be a little bit crazy to keep you from going insane.