PTLE won't launch - just bouncing in the dock

[jeppo1]

My Pro Tools LE has just started not launching. When I click it in the dock it just bounces indefinitely; I can't force it to quit, can't restart, just have to hold down the power button to shut down. I'm running Pro Tools LE 6.4 with an MBox on a G4 iMac, 512MB RAM OS 10.3.8. If I try to launch from Applications it still won't launch. I've tried uninstall and reinstalling - didn't work. I've completely erased my hard drive and installed from scratch - it still won't launch. It briefly launched once when I trashed all the relevant preference files, and allowed me to create a couple of dummy tracks, but when i tried to open a pre-existing session from my firewire drive, it got stuck opening up and got as far as blank white windows where the edit, transport and counters should have been. Still wouldn't quit. I've been through the Support pages and threads here and can't find anything quite like this problem.
I haven't added any new software or downloaded anything, it just started doing this one morning. I was using it fine the previous day. Also some other programs are affected - iTunes now quits halfway through playing the first song it finds.
Please help before i throw the damn thing through the window!