W7 won't boot past welcome screen (incl safe mode)

System exhibits slow reaction time to stimulus and a VERY long time to boot, has happened twice but first time removing all non-core processes and services on startup (including external graphics and sounds etc) besides networking fixed the error. Even when booting into safe mode without networking booting takes at least 4-6 minutes. Chance of being able to boot to safe mode is 60/40, when it's not going to boot the welcome circly thing freezes.
When it does boot into safe mode it takes at least 3 seconds to react to mouse stimulus, but reacts straight away to pressing the windows button for start menu. Reacts very slowly to actual typing and eventually crashes if you type enough letters.

E6600 2.6 Dual Core
2x 150 SATA Hdds in RAID 0 (cant remember model, will find if necessary)
Corsair 2GB DDR2 XMS2 DHX PC2-6400C4DHX TwinX (2x1GB)
HIS ATI Radeon HD 4850 IceQ 4 Turbo 512MB GDDR3

Any help would be appreciated, thanks.

P.s. WTF.