Quark repeatedly quits upon launching

After spending an entire day researching and testing, I'm thinking this is a hardware problem. Up until two days ago, everything worked fine.

QuarkXPress now routinely quits about 4 or 5 seconds after launching. The opening graphic appears briefly, then the spinning beach ball, then this message window:
*"The application QuarkXPress quit unexpectedly. Mac OS X and other applications are not affected. Click Reopen to open the application again. Click Report to see more details or send a report to Apple."*

Here's what I've done so far:

1. Trashed, re-installed Quark (6.5). No change.

2. Read through the window message report, caught this:
*"Exception: EXC BADACCESS (0x0001) Codes: KERN PROTECTIONFAILURE (0x0002) at 0x00000000"*
Went to Disk Utility, ran Repair Permissions three times. The first time it appeared no repairs were needed, the second time it took 15 minutes to repair a bunch, the third time no repairs needed. Still no change with Quark.

3. Read some more, then tested the RAM via Rember. Result: *"All tests passed!"*

I still can't access Quark. I went through every other app, and they all work fine. I can't launch Quark from either of my two backup hard drives (I guess apps necessarily run off the main HD?)

Other info: no hard drive is ever more than half full at any time. And yes, my G4 tower is fairly old, but the internal HD was replaced a couple years ago.

I still suspect a kernel panic per the message report, but I'm at the end of my diagnostic know-how. If necessary, I can do an Erase and Install or Archive and Install; I've done them before. But would like to hear about something more expedient first.

Any ideas?