Open the bios, there is usually something right on the first page that allows you to reset the bios to default settings. Do that, you have already reset the OS to its default settings, so it has to be hardware related. This could be many things, make a weak PSU, if your memory checked out, then I would test all the possible components including one by one stop all your USB based devices, like your printer or mouse and other things you have connected to your computer. Reboot after disconnecting each device and see if you can find the culprit. Including disconnecting all your DVDRW drives.