[DJ Specs]

Just to help a bit more...
What version of windows is it 95 or 98?
Do you know what Video Card you have?
And did you change the drivers of the Video Card lately?
Or what software or drivers do you think you installed around the time this began? Norton SystemWorks?

 

[DJ Specs]

Ok, forgive me if some of these things sound trivial.
First, make sure you have turned off the screensaver, you dont want this running when you use standby.
Second, I got this from the Microsoft help article:

SYMPTOMS
When your attempt to put Windows 98 or Windows Millennium Edition (Me) in Standby mode, you may receive the following error message:


Your computer cannot go on standby because a device driver or program won't allow it. Close all programs and try again.

If you close all programs and attempt to put Windows 98/Me into Standby mode again, you receive the same error message.



CAUSE
This behavior can occur if a program, driver, or hardware device is preventing Windows 98 from going into Standby mode. This is also referred to as a "veto" of the suspend command Windows 98/Me sends to the computer's BIOS.



RESOLUTION
To resolve this behavior, use the Power Management Trouble Shooter (Pmtshoot.exe) tool to determine which program, driver, or hardware device is preventing Windows 98 from going into Standby mode

 

[DJ Specs]

Ya, I thought it might have been the video card causing the trouble. Now lets see what we can do about it. First thing is we need to have the newest drivers for that video card. And from what I know, they are not being made anymore, so this might be a bit of a problem. However, I'll look around, and see what we can find, and if Danrak, (Our Drivers Expert) has any info that might help, please let us know.

 

[DJ Specs]

This is what is available:
3dfx Voodoo3 3500 Tools
Version 1.02.13
If this looks correct, or is newer than the ones you have now, download them direct from HERE!

Source: HERE!