Pc wont boot when i put in gpu

Probably not.

Not booting is not the same thing as not having a video signal at your monitor.

I'm guessing you didn't install the drivers yet, right? Boot your computer without your card, install your drivers, turn off, plug in card, reboot. After you do that, check your setting in bios to make sure your PEG(and not integrated graphics) is your default display.

Edit: And you made sure to plug your monitor into your video card? You didn't leave it plugged into your motherboard?

Sounds like you had the monitor plugged into the mobo. You need to plug it into the video card.

thanks it worked!