My custom build computer has been serving me well for a few years, but in the last three weeks, it crashes randomly in the middle of the average work (docu, internet etc), no blue screen, no error, system gone into reboot, sometimes back to normal, sometimes take a few reboot. I took it to the computer service, they replaced the secondary harddisk, it worked a few days, the last two days, same problem again, but the reboot takes longer, and a few more attempt, six times actually last night, can anyone suggest what could be the problem ? Many thanks.