Intel Latest BIOS

anyone plz help me
hi iam using intel 945GCNL orignal board with realtec hd audio ALC888
few days ago i got latest bios from intel's site and updated my old bios.
but when i started my windows xp there was no sound when i checked it deeply
it produces very feeble sound at one speaker & when i increased volume using windows
volume control a strange sound (like scratching something) was produced in other speaker.
and rest of speakers are producing nothing.Every software detect audio but no sound
I have done the following since then

checked speakers ther are workink
again updated bios
reinstalled windows xp even i installed vista
got latest drivers from intel's site also from realtek's official site
tried some old drivers too
but all in vain. now i am using an external 2.1 soundcard(PCI) of ESS but it does not fullfill
my requirements
my system is

Intel P4 3.4Ghz HT
1.5gb RAM
Nvidia gforce 8500gt 512 mb
250 gb WD hdd