4 year old computer will not boot up.

Hello,4 year old computer would not boot up. Fans and lights come on for 2 seconds and shuts down.
- Replaced Power Supply (no help)
- Pulled cards one at a time. Found computer would only turn on when video card is pulled. Put old PSU back in and bought a new video card (upon inspection, old video card had some blown caps)
- Installed new video card but same problem persisted but after several reboots, the computer came up, monitor turned on but could not get through boot process(it said CMOS has changed). Had to pull CMOS battery from MOBO and computer worked fine for a week.
- A week later the computer was powered down. Could not get it to turn on unless video card was pulled (nothing on monitor). Tried eraser trick on all cards including memory. Tried pulling memory cards to test MOBO for beeping but without memory and video card, computer would only turn on for 7-8 seconds and shuts off. Put all cards back into their slots and the computer would finally turn on (with video card installed too) but nothing appeared on the monitor. Finally, after about 20 off/on cycles, it booted up and windows began to come up on the monitor but then went black. After 10 more off/on cycles with nothing on the display, it booted up and everything worked fine. Computer worked flawlessly for three days.
- Woke up today, computer off. Again, when I push the power button the fans rotate for 2 seconds then nothing. Pulled RAM cards and video card. This time computer wouldn’t turn on even with the video card out, same symptoms. Did eraser trick and put all cards in and pushed power button about twenty times, computer finally turned on but nothing on monitor. Now when it turns on, one of the CD drive lights stays lit constantly. During normal boot up, they both should flash once. Powered unit down, pulled CMOS battery, reinstalled, computer turned on, nothing on monitor, one CD drive light stuck on. HEEEELLLLLP. Is this a motherboard issue? If I get the computer on, it works fine. Getting it on is a nightmare.