I covered once possible cause of this in my article Repeated Crashes During Boot but not all such crashes can be resolved using the approach covered on that page.
If you find that the system still crashes after a few minutes even after you have run a repair of the hard drive then the probability is that the problem is not with the hard drive at all but is being caused by something else. A good way to check for this is if you have a bootable DVD that you can boot your system from that doesn't rely on the hard drive at all.
There are a number of alternatives that you can use to perform this test but you need to either have a suitable DVD available before your computer suffers from this problem or have a second computer available to download and create a DVD to use. if you have the Easeus ToDo Backup software (even the free home edition) then it provides the opportunity to create a bootable emergency restore disk. All editions of Easeus Partition Manager except the free home edition also allow you to create a bootable DVD. Inserting either of these DVDs and rebooting the system will allow you to see if the system continues to reboot after several minutes when booted from the DVD instead of from the hard drive. Another alternative is to download a copy of Linux that can be run directly from the DVD (allowing you to test how that operating system works before installing it to your hard drive). One such Linux version that can be downloaded free is Ubuntu.
If you boot from a bootable DVD and your system still reboots itself after several minutes then you have eliminated the hard drive itself as the cause of the problem. In this instance any errors that the repair option is fixing on the drive are likely caused by incomplete writes caused by the system reboot and are not permanent errors on the drive itself. You can confirm that the drive is still useable after you fix the real cause of the problem by running another scan afterwards and having no errors found.
Another possibility is that the system has been infected with a virus. This is a likely cause of the problem if booting from a DVD does not have the system continuously rebooting but where running the repair doesn't allow you to boot the system without it rebooting itself again every few minutes. If you have a second computer you could try removing the drive and attaching it as a secondary drive in that second computer where it will then show up as a separate drive letter (E or higher) and you can then run the anti virus software on that computer against that drive to see if it can find any viruses. If you decide you don't want to risk a virus spreading to a second computer or you don't have a second computer the arranging for a professional to help out with fixing the computer.
If the rebooting continues to occur when you boot from a DVD then you have eliminated both the hard drive and its content as the cause of the problem. At this point the problem is most likely to be with either the motherboard itself, the processor, the memory or the power supply. Unless you have several identical computers available so that you can try swapping parts from a working computer until you find the part with the problem, it probably isn't worth you trying to proceed further with trying to locate the problem. By the time you mess about trying to purchase matching replacement parts to try (assuming the computer is recent enough for such parts to even be available still) you might as well simply buy a new computer. If the new hardware is compatible with your existing operating system you will be able to transfer your old hard drive into the new computer and either everything will be working again or you will be able to get it working again by installing a few new drivers from the DVDs supplied with your new system. If the new hardware is not compatible with your existing operating system then you will need to get a new operating system as well and will then have to reinstall all of your software onto that system.
This article written by Stephen Chapman, Felgall Pty Ltd.