Please Help. Having major problems

i was recently trying to flash my xbox 360 drive, and needed a long SATA cable. the one on my 360 was too short, so i decided to use the one in my computer. the only one in my computer was hooked up to my hard drive, so i switched to cables. well, that didnt work, and now i have a big problem. when i press the power button on my computer, it turns on, but nothing happens on the screen, and the lights on the mouse and keyboard dont light up.
it would be much appreciated if someone helped. Thaks!

 

Check and make sure you didn't knock something loose while you were changing cables, like a power cable or power switch cable.

Re-seat the video card.

 

Unplug the power cable from the back of your Power Supply and Make sure everything is connected right hdds, memory sticks and all the other stuff that connects to the motherboard. now remove the little battery on the motherboard for about 5 seconds and put it back on, now plug the power cable back in and turn the pc on and it should reset the bios and let u back in... hope it helps

 

thanks for all the help guys!
got the pc up and running again.