Crashing DB or Server?

Hello group,

I've got a really bad problem with my postgres DB and server.
It is a linux machine with 1GB of RAM and 2 CPUs.
The postgres Version is 7.4.

The problem is, that once the postmaster has started, the System is just
about useless. At least querys to the db are so slow, that it most often
runs into timeouts. First I thought something was wrong with my querys or I
forgot to close the connections. But this isn't the case, I cut all the
connections to the server so that there are no incoming requests. Still,
once I start the postmaster and look into the statistics of the top-command,
the IOWAIT parameter of all CPUs are at about 100%.

This is really weird, just a few hours ago the machine run very smooth
serving the data for a big portal.

Has anybody an idea what might have happened here?
I need a quick solution, since I'm talking about an live server that should
be running 24 hours a day.

Thanks in advance,
Moritz

PS: I'm not a administrator so I don't know if I have wrote down all the
relevant data. If not, please ask for it and give me a hint how to get them