I just bought an ati x700 pro (PCI Exp) to replace my old graphics card. I followed the instalation instructions and the card is working, but turning on the computer is the problem. I push the start button and 99 out of 100 times the graphics fan goes full blast, besides that it sounds like a normal startup except there is no output and the processor light is solid. After this i cant use the power button to turn it off. I have to unplug the pc and whenever I plug it back in 99% of the time it starts up automaticaly locks up again. Sometimes I get lucky and get it to start up, and it runs fine. What is happening?
How can I fix it??? 
How can I fix it??? 

. I missread and now see you said turning on your computer. Anyhow dont pull the cord if you can help it as its a crap shoot wether your going to do big damage to your PC. Rather hit the power button on your power supply if it's got one (this is not great for the pc either)