Mac OS X and programs keep crashing...



I own a Power book G4 with Mac OS X Tiger. My computer has worked perfectly until yesterday when strange things started happening. Firstly, intermittently, but quite often, I would access Safari and the application would unexpectedly quit along with the message that it had unexpectedly quit. I would then try to reopen it and the same crash would occur. I would then try using Firefox and the same thing would occur.

As well, along with the above, sometimes the computer would either completely stop responding or the computer would display a message saying in a few different languages that I had to put my finger on the power button and hold it down to restart the computer.

I ran the disk utility but the messages it gave me were:

"Mounting Disk(S, "Checking HFS Plus Volum.",0)
Checking Extents Overflow file.
Checking Catalog file.
Checking multi-linked files.
Checking Catalog hierarchy.
Checking Exctended Atrributes file.
Invalid leaf record count (in red)
(It should be 2 instead of 196)
Checking volume bitmap.
Checking volume information.
Repairing volume.
The volume Macintosh HD was repaired successfully.

Repair attempted on 2 volumes
1 HFS volum repaired (in green)
1 volume could not be repaired (in red)"

Can you help me get my mac working properly again?
Between today and yesterday have you done anything different with your computer? Power outages, improper shutdowns, changed any hardware, etc?
Try booting off the Tiger DVD and running Disk Utility repair from there. Quite often disks cannot be repaired while you are using them.