Segmentation fault - help please -

[homega@vlc.servicom.es]

Hi,

I quit x-window and try to connect as I did a while ago:

$ pon provider
hda: irq timeout: status=0x50 { Drive Ready SeekComplete }
/usr/bin/pon: line2: 5552 Segmentation fault	/usr/sbin/pppd call
${1:-provider}

try again to the same results (just the 5552 number changes to 5562, 5572,
5574, 5587,...), so I try to su:

$ su
Segmentation fault

$ startx
-X11TransSocketUNIXConnect: Can't connect: errno = 111 giving up.
xinit: Connection refused (errno 111): unable to connect to X server
xinit: No such process (errno 3): Server error

$ mutt
Segmentation fault

Other commands such as cd, ls, less, or lynx do seem to work fine though. 
Then I type `exit' and reboot, and everything seems back to normal.
What went on?

TIA

Horacio