You could try the built in disk defragmenter and see if that solves the problem or you could go into Safe Mode, this can be F2 key on your computer (you have to find which key does this and do it quickly before Windows 7 starts up) and see if this boots up in safe mode, once inside you can see if it shuts down then or not, it could be a faulty driver issue that needs uninstalling, think if you have downloaded or installed some software recently that may cause your pc to malfunction and shut down. Try last known good configuration, this could be your F8 key in Advanced Boot Options, google this if your not sure. Also listen to sounds or beeps. Is there a beep when the computer loads up normally, one beep means it's fine. This should go into POST (Power On Self Test). Try this as well as Click Start, type go to Accessories, right click, run as administrator and type chkdsk/f. Also try sfc /scannow using the command line and see what happens then. Another option once could be to test your memory, there are tools to download for this such as memtest, link here http://www.memtest86.com/. Failing all this try a factory reset, but try and back up all your files, photos etc before doing this to an external hard drive. If this then get a replacement hard-drive as this could be the problem. Hope all this helps.