I was very used to putting my computer in Standby in XP and Windows 2000, because it let me resume what I was doing very quickly, however, after reformatting and installing Vista Ultimate (Build 6000), sleep mode seems to have a problem. When I select sleep mode in the shutdown menu, my computer monitor will turn black and it will say "No Input" like the computer is in sleep mode, but the fans and lights will stay on in my case. The fans then slow down slightly and then after about 5 seconds or so my fans spin at full speed and my hard drive clicks like I'm booting up without me touching anything. I'm returned to the login screen- and when I log in everything is the way I left it. I've reinstalled Vista several times, reformatting each time, but the same thing happens when I try to put my computer in sleep mode.
I am currently running:
AMD Athlon 64 X2 4200+ At 2.33 GHZ
Motherboard: ASUS M2npv-vm
1GB Corsair VALUERAM DDR2 533.
Samsung HD160JJ, MAIN BOOT
Some Hitachi out of another computer
And a really old maxtor
BENQ 1655W DVD+/-
Really old CD-ROM 32x
With these same specs I could go in and out of Stand By in Windows XP and 2000 just fine.
I have the same motherboard as you and it is usually a hardware issue. Make sure you have the latest Asus m/b BIOS - only the last BIOS update had S3 fixes related to harddisks. Also, are you using SATA or IDE - per the ASUS forum, many people are having issues with SATA versions on the m/b and standby/sleep. I am personally waiting on a BIOS update from ASUS to fix a few memory stepping issues with the board that they said they would release shortly after Vista was released.