I am not an expert so take this advice at your own risk.
If you have a copy of all of your files still on the external HDD, then I would say since your errors are from trying to load Win7, then format and reload Win7. test internet connectvity before adding your files back to the computer. if good, double check device drivers and download any that you are missing. note that you will likely need a chipset driver for your motherboad/cpu, drivers for any expansion cards (video, audio, other), and odds-and-ends drivers for devices such as printer or game controllers or maybe even mouse and keyboard if you use fancy ones.
Once you have good internet connectivity, drivers all loaded and everything working, then its time to add your files back in. doing things like that would let you get the system working and add in device drivers and devices one at a time until you either get a problem or get it all working. if you get a problem, you know the last one installed was where the problem arose.
install devices drivers starting with the most important: computer first - cpu/motherboard chipset drivers, then expansion card drivers. If your computer came with CDs for these, use them. If not, use another computer to download the ones you need. Sorry, I am no help in finding the correct ones - someone else will have to advise on that. install usb and other external devices last. they are not important to the system for it to function so they get to wait til the end.
Hope this helps. Again, I am not an expert, do some reading before blindly running wild on a broken computer. Or, maybe the next poster will be an expert.