It sounds like your computer is getting the BSOD and has the automatic system restart upon crashing parameter enabled (you can check to see if this is the case, typically by repeatedly hitting "F8" as your system starts up). If this is the case, you can do a google search on the stop error information to better discern the issue. Hardware-wise though, it could be RAM, video card, HDD, or any new installed peripheral. Honestly, this sounds more like the handy work of a virus to me. Chances are, it has corrupted/deleted the registry files required to load Windows. As it seems though, your computer is passing the POST (Power-On Self Test), starts to load Windows and then reboots.