BSOD 3x in past month. Entire system now malfunctions. Please advise

I am experiencing lag times that are incredibly slow. When I log on it takes almost 10 minutes before my desktop appears. Any software program takes a long time to open and always kicks back errors that I have clicked "do not ignore" including I9. Outlook won't load my folders anymore. All folders: documents, pictures, music take up to 20 minutes to upload. I suffer watching a green bar slowly creep across the menu bar with no results. I also ran a complete Windows Defender-found nothing, defragged my hard drive, checked recent updates-found none. My computer also has started restarting itself (no time pattern) and I've had the "blue screen of death" appear three times in the past month-all times required hard reboots. Took all the advice found in aother forum about lag times to try resolve my issues: Booted in safemode-took almost as long to upload; Ran SFC/SCANNOW in command field-results returned normal, no integrity issues found. My computer is less than a year old. Gateway says its a Microsoft issue because I changed from the OEM to my own Windows 7 Professional (discount because I'm in school). Had a computer tech look at it & he says it either my media center shutting systems down or my cpu is overheating or my video card is defective. Beofre I have someone dismantle, change, or delete anything I thought I would check with this forum for advise before I let anyone "fix" my computer.

Did reset my BIOS to factory defaults and that seems to speed up my Windows a little bit. But then I got the blue screen of death again and now everything is running slower than honey from a bottle in January in Alaska! I really hope your forum can help me. I'm desperate at this point.