Explorer shows the sum of all files to be 145 gigs (this includes C:\Users, Program Files (x86), Program Files, Windows, ProgramData, Emergency, Drivers, etc.). However, if I choose properties C > Properties, it says I'm using 470 gigs (I know this to be correct because if at one point things got to almost 500 gigs, my limit, an things slowed to a crawl). There seem to be some hidden files somewhere or some corruption somewhere but I can't find it. I got ride of restore points and shadow files but that only bought me 10 gigs. Virus scan with MS Security Essentials showed no viruses. The checkdisk utility ran and found things to be OK. Any ideas about how to recover the hidden 300+ gigs?
Open Explorer and set the view properties so that you display hidden files and system files. Then do a search of drive C: with a size filter "size:>1GB" (pick your own value here). Have a look at the results and see if there are any abnormally large files that are normally hidden.
OK, I've done that but I don't see any hidden type files. There are some large files (130 - 450 Megs), but they are files I created and are included in the folders weighing in at 14) Gigs. In the meantime Explorer has slowed to a crawl again.
It should always be safe to delete files in the Temp directory. Looks like you've found the culprit, but it seems a little strange - and it would be nice to know what caused it.
Do you have a current backup of your data - just in case? If you're nervous one possibility would be to rename the file - say to tmp9991.tmp.old - just to make sure that nothing breaks, and then delete it when you are sure it's OK to do so.
Although that doesn't quite account for all the missing space the rest is probably hidden and system files that Explorer wouldn't have been counting.