Hi. I have a classroom of 16 iMacs which are about 5 years old. One of the iMacs starting taking about 10 minutes to log anyone in. I tried running Disk Warrior, fixing disk permissions, and repairing through disk utility. Nothing worked. I then installed Snow Leopard over the install and that seemed to fix everything. The only problem is that when I install any updates to get the OS up to date it goes back to taking forever to log anyone in. Any ideas? I about to wipe the computer and start fresh.
That would be my idea at this point, backup any data you need (a failing HDD is not impossible given the symptons). Erase the disk and reinstall Snow Leopard from disk.
If in doubt about the hardware, see if you can run the Apple Hardware Test. See: Intel-based Macs: Using Apple Hardware Test for details.
Note that if the HD has been erased, you may need the original (gray) discs that came with the Mac (or the same model and build period), as noted under Additional Information there.
Run the Extended tests (that may take an hour or more, depending on how much RAM you have). Write down any error code(s) it shows.