[SOLVED] Computer working for years now sending no signal to display

[Cobbl3]

I just bought my best friend's homebuilt computer which has worked for years, yesterday we booted it up and reformatted the drives with no problems. Then I took it home and installed some of the har drives from my computer and tried to boot it up but now it sends no display to my monitor? (lights are on and fans are spinning)
I'm really not sure if I've done something wrong whilst managing the drives (the boot drive is untouched) or if something went wrong when transporting the pc. Anyway I'm not sure what could have caused this as all the ram and connectors have been untouched.
Any ideas are appreciated!

 

[swissc]

Have you tried a different cable and both a different display port on both the pc and monitor?

 

[Daniel_pt]

Your using a different monitor then the one your friend had?
Have him come over with is monitor. If it works, the problem either is with your monitor, the cable you're using or the port being used vga vs dvi vs hdmi.