Strange problem with IO or file system or what?

Strange problem with IO or file system or what?

On a SLES 11 SP2 32-bit system I'm seeing a strange problem. It's as if
the OS can not open a file from the beginning of the file.
Say I have a file that is 200 lines. If I cat or more or vi the file, the
system just hangs. The process never even starts. I can tail the same
file, but only up to about 100 lines. tail /path/to/file and tail -n 25
/path/to/file works, but tail -n 100 /path/to/file does not work.
Even an ls command on a directory with lots of files fails.
There is plenty of disk space. The file system is read/write. An fsck did
do some fixes but the problem still exists.
Any help is greatly appreciated.