I've got two hard drives and I've set the order of priority for booting, but for some reason the BIOS keeps on resetting and losing this setting. I was tbhinking it's the battery, but then the time & date in BIOS are correct so it can't be the battery? ANy ideas?

are both the drives sata ? or is one ide and the other sata ?

flash your bios to a later version.

as mr_psi said, goto your motherboard manufactures website and locate your model. There then will be a section under Downloads or BIOS updates where you will be able to obtain the latest version for your BIOS.

Sounds like a fault in the bios.

* Reset to factory defaults - Enter BIOS, there will be a function key to reset BIOS back to factory defaults.

If that doesn't work.

* Clear the BIOS - Pull out the CMOS battery, and the power cord. Leave the computer for a few minutes then put the battery/cord back in.

Or as suggested above flash your BIOS to the newest version

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Osama Bin Hooning
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Perth-Wrx

Try switching SATA mode or HDD mode to compatible.

One is IDE and the other is SATA

are the jumpers right on the drives.. ?

Im leaning towards a corrupt BIOS as well.

Does it have a boot order menu (ie press f10 during POST and it brings up a little menu just after POST) ? if so, try using that. One of my old mobo's does exactly the same thing until I use that menu (it'll be ok the first time, but then "loses" its settings)

oh, and as for updating the BIOS, read the change log. Normally BIOS updates are updating micro code, errdata, tweaks for OC'ing etc etc. Boot order is kinda simple in the grand scheme of things and wont really change between revisions (unless you're dealing with earlier (~2002-03) systems and the change to 48 bit LBA addressing)