I recently got a new hard drive I tried it the computer works and it turned on but I changed the screen setting and it was out of range so I fixed it by plugging in another monitor into the computer which worked but after I plugged everything back in to the way it was the computer wouldn't turn on. I'm pretty sure the power works cause the fans sometimes spin and there a little green light glowing inside but it won't start. What is wrong with it it worked this morning?

Computers act weird sometimes, I've had a lot of PCs do that to me. This is what you can try:

1. Unplug the power cord, wait a minute, then press the power button for at least 10 seconds. Plug everything back in, and see if it powers on.

2. Reset your BIOS - Just in case the motherboard has had some kind of problem, this will reset everything to factory settings.

3. Make sure the Power Supply is good, do you have a PSU tester by any chance? If not, here's a good one: http://www.newegg.com/Product/Product.aspx?Item=N82E16899705002

4. Try the motherboard outside the case like shown in this pic: http://www.letheonline.net/images/motheroutside.jpg

5. Report

ok its fixed the 10 seconds thing worked.

Awesome!