Noob needs help

[Captain Carling]

Hi, im new to the forum so go easy

I have a problem that i cant figure out. I have four hdd and two of them are sometimes not showing in the bios. C and D drives are always there, but E and F come and go.
When ones missing, the hdd light on the case is constantly on, as if its working overtime or something.
Im using windows 7 64bit and the drives are western digital via sata.

Anyone got any ideas please

 

[Captain Carling]

I haven't tried them one by one yet and the mobo is an Asus P5Q Deluxe

 

[Captain Carling]

I have a q6600, a nvidia 260 gpu and a corsair 600watt (cant remember if its a 600 or a 650)
This set up has been working fine for a couple of years now, its only the last couple of weeks its been playing up