Master & Slave HDDs not recognised

Hi Guys,

My PC is not recognising my HDDs (master & slave). I've been running my self-built system for about 3 years and have made no recent hardware changes. It was running fine until the other day when running Vista I started getting 'Windows Host Services' error message which would just disappear after clicking OK which I didn't think was a huge problem (not sure if this is related).

Next time I tried to turn on my PC, and attempted to boot Vista, I got BSOD (Machine_Check_Exception). It then began freezing 9/10 times on the POST screen. If I waited a few minutes it would progress past this point only to receive the message 'DISK BOOT FAILURE - INSERT SYSTEM DISK'. It does, however, recognise them in the BIOS

Things I've tried:
- Booting into XP & Linux using live CDs - neither display the HDDs.
- Reinstalling Vista - cannot find HDDs
- Reinstalling XP - keyboard frozen where you select repair/install etc.
- Reset cmos
- Reset BIOS to optimised settings
- Disconnecting both HDDs & power on - it loads past the POST screen every time.
- Changing RAM to different slots
- Using another HDD to install a fresh copy of windows - not recognised, same problems
- Tried a brand new cable

Hopefully I've given enough info here & not missed anything out

All suggestions are much appreciated!!!

_______________________________
MSI K8N Neo4 Platinum
AMD Athlon 3200+ 2.0 GHz
2 x 512MB DDR 3200
Dual Boot - XP (SP1), Vista Ultimate