HELP: partitions keep disappearing

flex

This is the weirdest thing: partitions keep disappearing and revert to unpartitioned space.

Bought myself a 200GB Maxtor HD for one of my older computers and want to install win xp on it, so took the computer totally apart. Formated the HD, installed win xp, but after a few reboots, the partitions disappear.

Hardware connected:
P4 1,5 GHz
384 MB Ram
200 GB Maxtor HD
Siluro T400 64MB graphics card
DVD
network card

Can anybody help me, I'm totally lost.
Thanks