|List your system specs (make and model number or if custom, detailed components list).|
Tell us what graphics card.
What is your power supply (make and model number)?
Is the card a refurbished card, an open box special, purchased used, or from ebay (or similar)? This can matter.
Have you tried downloading the latest video driver for your card/operating system?
Have you tried downloading the second from the latest video driver for your card/system?
Are you sure you are selecting the correct system (32bit/64bit as well as operating system matters)?
Underclocking should not be necessary, even if it is a factory overclock.
Answer these and we may be able to help you.
You have to be a little bit crazy to keep you from going insane.