Upgrading GPU

[grabthaak47]

Hey guys im new here and not so good with computers.... But Im having trouble uninstalling my Geforce GT 620 and installing my XFX Radeon 7750. I can get the GT 620 card out and the Radeon 7750 in, but when I turn on the pc afterwards... my monitor says "no vga" or something like that?
Please guys help me out.... I just wanna game!

 

[Azn Cracker]

either your card is a dud or you didnt plug something in corrrectly