Cpu: Intel i5 4430 3.0ghz
mobo: MSI z87-g43
Ram: 2x 4Gb DDr3 1600mhz
Gpu: HD4670 1gb DDR3
PSU: coolermaster thunder 600w
HDD: WD blue 1TB
optical drive: Samsung Dvd rw

I have put all my parts together and into the case. when i turn on my pc for the first time everything seems to run properly, all fans and all lights are on. i have my display plugged into my motherboard, and my mouse and keyboard plugged into 2 usb ports.

The computer carries on running for a while but the display says no signal?
why could this be? its not the monitor because its always been working fine? could it be that some of the hardware is not installed properly? should i remove my gpu even though i have nothing plugged into it?
Any advise would be appreciated. Keen to get my pc up and running