|retrace all the steps you took when transferring the kit. Mkae sure all cables are secure and connections that need making are made. |
does your graphics card require additional power (4pin molex)? if it does is that connection secure?
Did you wear an anti-static strap whilste working on it? Or use an anti-static mat?
Does the PC start-up normally and give the ok beep? (one single beep)