Not much information to work with, but if you are getting reboots after the computer has run for a few mins., I would look at a few things. First I would check for heat problems, open the side and with a can of compressed air blow out all the dust you can find, CPU's heatsink and fan, Vid cards fan, motherboard. Any dust you can see. 2nd I load the newest drivers. I assume you have defrag the hard drive and have a virus program running.