I also have an nForce4 onboard chipset on my Asus A8n-e.
nForce4 has real problems with mtkflash its very hard to get it working.
I did manage to get it working by using diff combinations and flashed the drive with bad firmware! (Didnt put in my drives cd-key on the modded firmware)
Luckily I have a backup of the original firmware but, like yourself, i cant connect to the drive again
So today i ordered thishttp://www.shinyhardware.co.uk/products/product.asp?pid=1264
Its a tenner and its the reccomended PCI Sata card thats compatible to flash both 360 Samsung/Hitachi drives
I'm waiting anxiously for this to arrive so I can repair my drive
I suggest yo get one of those cards mate, nForce4 is a pain in the ass, btw there is a way of fixing it but you have to have the right BIOS (I dont) what BIOS is your mobo? Is there anything that says SATA spread spectrum on it? if there is set it to down spread, that has worked for alot of ppl..good luck..