New GPU no signal to monitor

Hello,

I can't get the new GPU (Ati Raden 5770) to get signal out to my monitor.

I have a P5LP-LE MOBO and the PC (an HP one) came with a TV tuner card.

Anyway, I'm running Windows 7 and I disabled the integrated graphics card. Then I turned off the computed, disconnected the power and took the TV tuner card out (first I had to unlatch a pin that was hooked to it).

Then I took my 5770 and inserted it into the PCI Express slot. Next I hooked it up to my new PSU (Cooler master, 600W).

Ok, so far so good. Right? Well, here comes the problem. I start the PC and all the fans, even the 5770's one, are running however my monitor goes to sleep after saying it detects no signal.

What did I do wrong? How can I correct this?

I mean, my monitor has a DVI out slot and I tried hooking the cable first to the bottom slot of the card and then to the top one but it made no difference.

What should I do? I tought that maybe I did something wrong so I got the 5770 out and reinserted the old tv tuner card. Monitor got signal.

Taking the chance provided I went into the MOBO and under the GPU options I only get to sources PCI or Onboard however I know the MOBO has a PCI Express slot.

Please help me out, I've been at this for 5 hours straight and it's gotten so bad that I want to cry (seriously >.<).