an8 fata1ty and 4800+ isssues

hi guys i have this system:

Manufacturer: Custom with ABIT FATAL1TY and loads of neons
Processor: AMD Athlon(tm) 64 X2 Dual Core Processor 4800+, MMX, 3DNow (2 CPUs), ~2.4GHz
Memory: 2048MB RAM
Hard Drive: 80 GB
Video Card: MSI NX7800GT NVIDIA GeForce 7800 GT
Monitor: LG FLATRON M1710A
Sound Card: SB X-Fi Audio [9C00]
Speakers/Headphones: Creative headset and Philips 2.1 speakers
Keyboard: Saitek eclipse
Mouse: mx518 logitech
Mouse Surface: nemisis inferno mouse mat with
Operating System: Windows XP Home Edition (5.1, Build 2600) Service Pack 2 (2600.xpsp_sp2_gdr.050301-1519)

It is water cooled using a thermaltake bigwater system.

whn booting i get the message "system is in failsafe mode please check CMOS setiings in BIOS and restart" which i have done and can see nothing wrong ( i think) but i get LOTS of Blue Screens Of Death! when i am using the pc (it can be made to boot by hitting F1) i have loaded failsafe settings and optimised defaults and still have probs.
The system has been reinstalld and still i get the same probs!!!
I have run memtest which showed no faults/errors (on my 3rd pass whilst writing this)
The fault seems more prolific when the system is idling and not whils playing a game or running demanding apps (like WoW!)

any ideas or info would be v helpfull