650 watts is way beyound your current needs.  400 to 450 is adequate, especially for the older video card you have, which should not require more than 350 watts.

Your drivers may be too new for your older video card.  Uninstall the current drivers, go back to the ones that were installed with the system when you got it.  

Check your video card and see if you have a heat sink or fan.  If a small one get a larger fan and apply some Silicon Arctic Circle Heat Paste.

If that does not work, then try to swap out your video card with a newer card and see if that is the problem.  

Add new heat paste to your CPU, and check the temperature monitor in your BIOS after running two hours.  If above 140 degrees you are having a heat problem, and the B plus may be failing.  

If all of that does not work, then Reset your BIOS to Manufactuer Defaults.  You may have to check the Mobo manual or reset using the MOBO CMOS shorting posts.  

Get a new Motherboard battery, they are cheap.  Otherwise, you may have a failing CMOS BIos chip.  Hopefully not!!!  

Damaged resistors and capacitors happen all too frequently.  Most boards are coated and so it usually does not make any difference how much dust accumulates.

If you clean the MOBO, air can only, no brushs, no solvents, and no pressure.  

I think that should get you started. 

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