> I don't know what's wrong with that
> particular site?

a) even slight differences in amount of traffic,
users, transactions etc. may cause this

b) Maybe the network wiring has grown old or
become damaged? You know it requires highly
specialized, sophisticated electronic measurement
equipment to verify the integrity of twisted pair
wires.

Just do as they told you, throw out the server hard- and software, and
possibly renew the network wires. And check for viruses ...

Cheers,
Tobias