After updating Firefox and Parallels, my iMac running 10.6.8 wouldn't boot normally, instead giving me variously blue screens or gray screens. I have been able to boot into safe mode, and have made a Time Machine backup, and also ran a Verify on the Disk Utility. The Verify program reported the following: Verifying volume "Macintosh HD" Performing live verification. Checking Journaled HFS Plus volume. Checking extents overflow file. Checking catalog file. Incorrect number of thread records Invalid leaf record count (red) (It should be 1790705 instead of 1790704) Checking multi-linked files. Checking catalog hierarchy. Invalid directory item count (it should be 35 instead of 34) Checking extended attributes file. Checking volume bitmap. Volume bitmap needs minor repair for orphaned blocks Checking volume information. The volume Macintosh HD was found corrupt and needs to be repaired. Error: This disk needs to be repaired. . . . then use Disk Utility to repair this disk. I suppose that I can try and repair the corrupt disk, but I was wondering whether upgrading to Lion -- which I was planning on doing anyway -- might cure this problem as a result of the new installation. Or might upgrading to Lion with the disk in this condition result in disaster? If upgrading without repair is a bad idea, what is the best way to repair the disk? I have the Snow Leopard Install DVD. Should I use the Apple Disk Repair, or would I be better off with a third party product. In any case, if this all goes wrong, how much faith should I put in my TM backup? Would it be worthwhile to back up individual files to a secondary backup before proceeding, or is the TM backup pretty reliable. Thanks in advance.