I suggest you to try MemTest86+ to check your RAM for failure. Also, try to took out your CPU and put thermal paste on it, be sure that all pins are fine and put CPU back on motherboard connector. Get some HDD diagnostic utility on web and check performance of your HDD. You can use NERO's tool, if you using Nero for burning CD/DVD's. Or took something else from Internet.
Try to clean your computer from dust, and took Motherboard battery out. You'll reset BIOS settings by doing this step, which is fine and I suggest you to do that. Or, go BIOS and choose Load Optimized Defaults, press F10 to save and restart your computer.
If you still have problems let me know.