I took the motherboard out of my HP520C, and put it into a new tower, cuz the power supply was bad. Now when i boot computer up, i get a cable is disconnected, no input signal. Now i've checked my monitor and that works fine on my other computer. So, i know its not the monitor. I'm thinking that the video card bit the dust. I have onboard video on mobo. If it is the video card, once i install another video card, will i still have to disable the onboard video? Could my bad power supply have shorted out my onboard video? Also, on the old power supply, there was a power fan connector next to the ATX power plug. On my new power supply i dont have that 3 pin adapter. Could this be my problem?

I'm desperate please help.Why didnt you just replace the psu?The motherboard needs the correct psu to function properly.What type of board is it and what type of tower are you trying to put it into?Its an Asus A7V socket A motherboard. The case was overheating and i needed to transfer it out of there. Major cramped in there, no cooling possibilities. I'm putting it in an Antec case, with 350 watt power supply. I have to have a certain power supply , besides just an Atx ? Thats what the original power supply was an Atx, but its made by Hewlett Packard. By the way thanks for replying so quickly.  What makes you think the power supply was bad?
What makes you think the case was overheating?

The standard case is not that small.
on some older models the hardware had alot of proprietary stuff which made it hard to swap stuff,especially power supplies.all the new supplies are now made the same and have the correct voltages and grounds to the same pins so now they all conform.some older psu's would switch the 12v supplr to a different pin and if you put a new psu in and the 12volts went to the wrong pin> goodbye motherboard.Dell and HP were the worst offenders of this.Hello friend how are? Do another thing. Remove all of the RAM sticks from your board and clean any dust from both RAM and RAM slots on motherboard. Then agian put them in their respective slots.
Yes in ome cases, you have to disable onboard VGA if you have another card. If you have, then remove the card from PCI slot if you have PCI VGA card or whatever it is. Cleean both card and PCI OR AGP slot and then put it again.
Now urn your PC ON and I m sure you will get display.
Take care of yooou and others and be happy
Bye...
Dur-E-WahabYou know what? I think you have something there. I had removed my memory to transfer everything. However, heres the kicker, I put everything back into the HP case including the bad power supply. (I gave it a good cleaning.) Now i got it to boot once to the hard drive. So, then i put the dvd and cdrw in and now im back to no display again. I'm not getting a hd led LIGHT either. Their is only one way to put the power, led, switch in cuz it comes together. I know its something stupid but ive spent 6 hrs with this and im fed up.
To answer your question about a bad power supply, the fan is really rattling in there and its only a matter of time. Also looks are deceiving about the case. They didnt make it big ENOUGH inside for air to flow properly. The floppy has its own drive case, and they put an air intake over the back fan over the processor. Really crowded. Some guy WANTS to charge me $35.00 and said its really easy to fix. Someone must have some idea what im doing wrong. CMON, save me $35.00 lol