Windows 7 may not boot smoothly when you transplant the drive from homebuilt pc to optiplex.  the motherboard and cpu may be too different to support a smooth transition.  you may try but Win 7 may or may not crash on optiplex running Win 7 previously installed on home built pc.  when it crashes you can try to let it repair but no promise it would work. Re: I think the motherboard etc is busted. try clear cmos on the home pc and replace cmos battery to see if it can be resurrected.  if really dead and optiplex can not run Win 7 on drive, one option left is to replace home build motherboard if feasible.
My home built W7 computer blew the 5amp fuse when the power supply went pop. The hard drive is intact but I think the motherboard etc is busted. I tried a new power pack but it is still dead. I can see the hard drive contents when I put it in a usb cage attached to another computer, I have an Optiplex 7020 SFF which I would like to put the drive in - not just because of the data but because of the programs that are installed, in particular a copy of Sibelius 4 Music Software installed on it with a rather complicated set-up for getting the scores to play back properly. So that is the program files and user settings and instgrument sounds which I suppose could be in appdata.  I also have Sibelius 6 installed. So that it the problem. I am used to cloning hard drives with Macrium but the problem is that the hardware, motherboard and all the attachments are all different. I also have a Macrium image of the drive Basically is it possible to transfer not just the data but the program files and appdata settings onto new hardware? Many thanks  
Optiplex 7020 SFF install HDD from busted computer