Just to be sure you are running an intel motherboard right? i7's are intel made. if your motherboard is AMD then your screwed because AMD + intel don't go together. No signal could mean a bunch of things. Graphics card drivers might not be correct. Example. you said you have an older win xp HDD in there. now if you just put this hard drive in, with the OS already installed after your pc was built, then yes, everything is messed up and will not work. Because when you build a computer, most of the time you install the OS new as well with a new HDD. When you do this the HDD and OS automatically pull the drivers from your mobo (with new parts, the old parts you used to have to install all by disk, not anymore) and install them on the HDD. BUT you took this HDD from a differnt computer, then it won't work, because this HDD will have the drivers and software from the other computer. The only way to fix that then, would be to install the OS fresh.