What would be the cause for a HDD and sometimes the DVD to show up at boot one, time and then not show up untill 10-15 boots later? Totally random too, can have both, then just one etc.

I've been trying to install XP that was perfectly fine before the attempted install and installed fine untill it need to use the HDD and then it hangs, gives errors etc.

Tried another HDD and same errors occur.

Took the HDD to another setup and was able to install windows onto it without any problems at all

Rig is a Shuttle SN85G4V2.