Computer continually turning on and off
Good afternoon. Earlier today, I decided to open up my PC and do a little bit of dusting. I took out the GPU and CPU to make sure I got as much dust as possible, but after I re-seated everything, it won't start. What'll happen is when I press the power button, it'll light up and turn on for 3 or 4 seconds and then it will turn off for 3 seconds and turn back on and it'll keep doing this until I manually switch it off on the PSU. I've tried resetting the CMOS, taking out and putting the battery back in, and even trying a different PSU/GPU, but to no avail. Maybe it's the CPU? Do I need new thermal paste to re-seat it properly? I didn't peel it off of the heatsink, but I'm just wondering. It might be the mobo because that, the RAM, and the HD are the oldest parts (3-4 years old) in the computer. The CPU and PSU are pretty new still. Any information/help would be appreciated. Thanks!