Windows 7 Memory Diagnostic Tool

I am running windows 7 for long time and I havent came accross this yet , so this is what happend in shorter version, I was using my computer when the screen just went black. I just tought to myself its probably something wrong with my memory so i ran the Memory Diagnostic Tool ,I picked the first choice that it recommended "Save work and restart the system". The computer restarted, and the tool started to work after 15-20 minutes it was nearly done 90 somthing , i just went down stairs to get a drink and when i came backed upstairs i realised that the scanning is at 8% again , I tought maybe thats how it works , scans 2-3 times , i lefted the computer working over the night when i waken up the tool was still working , went to work , came backed and the tool was still working , i just said to myself this has to be wrong , i unpluged the pc left it over the night. Turned it on , the diagnostic tool started itself again , The scan was neraly over when just again i realised that this think goes in infinity. I pressed the " Esc" button as it said to finish but when i press the button the scan just resets and goes from 0% again, It doesnt want to let me run safe mode or anything else , only go to bios set up.