There are ways to find what bits are missing - I can't remember now (blame my age) - might be something like SFC /SCANNOW from a CMD prompt.
When I had a hard drive glitch on my desktop PC a week or two ago, CHKDSK (or whatever that's called now) ran automatically and deleted four files that it said were corrupt. It told me the names it was deleting, but they meant nothing to me, and it rebooted before I could write them down. The machine still didn't work after the CHKDSK but the error messages were different.
I tried the Win7 disk and "reinstall/repair". That said it had done the job, but the problem remained. Google was no help either.
Then I ran the program (SFC or whatever it was). It didn't fix it, but it produced a long (about a megabyte) test and error report. It said, right at the end, that four files were missing (that same four - I recognised the names). I tried to reinstall them from the Win7 DVD, but it wouldn't do that.
I fished out a memory stick, and copied the four off the laptop and onto the desktop. Job done, desktop back in action.
Then the power supply started emitting smoke and smell, so that's off until the new power supply arrives. I have a spare somewhere, but in all the chaos of moving I can't find it.
BT haven't managed to get us a telephone at the new place yet anyway. It was supposed to happen on April 6th, then on April 19th, but each time ... nothing. Apparently, it needs "Openreach" to do something, and they are not contactable other than by e-mail or carrier pigeon. "Customer facing" they certainly aren't, and BT Customer Service tried for an hour to contact them and failed. So we wait for the boon of Openreach.
I bought a Voda dongle to tide me over, but the GPRS signal is on the limits. I get up to the dizzy heights of 20kbps sometimes, 5 kbps is more usual. 3G has not, of course, percolated to such rural parts.