Ahhh what is wrong with my computer???? Please help!!!

A few weeks ago I took my computer apart to install a new heatsink. Shortly after, I began having problems where my monitor would not come on when I turned on my computer (hdd light never started flashing, so I know it wasn't a gpu issue or something). It would take 5-10 tries before it would work.I figured I must have done something wrong when putting my computer back together before, so the other day I decided to totally take it apart and put it back together again. Once I finished I pressed the power button, but the problem persisted. After the 10 or so tries, the display finally came on, but it froze at the BIOS screen. I tried again and it got passed the BIOS screen, but my computer just randomly restarted while loading windows. I tried again and it said ''Windows failed to start This could be because of a recent hardware change.'' I kept on trying and finally got it to boot to my desktop. But several hours after using my computer I got the blue screen of death. So now, every time I use my computer, it will either freeze while booting up, restart while booting up, or get the bsod while at the desktop.Does something sound defective?? THe fact that all my problems started upon taking apart and putting my computer back together doesn't seem like coincidence. I did use thermal paste, and my cpu temp is similar to what it was before I ever had this problem. What is wrong???? Ahhh what is wrong with my computer???? Please help!!!
were you EXTREMELY CAREFUL when removing the heatsink? i would check the pins on the cpu. i would also unload a can of duster inside the case for good measure