Standby resume no longer possible - help!

[Ardor]

Since a while it's no longer possible get my PC out of standby modus.
How did it work in the past?
- click standby
- Screen shuts down
- PC became 'quiet'' ( led's keep lightning of of course)
- Back active again after pushing the ON-button of the machine

What is happening now ? ( wrong)

- click standby
- screen shuts down ( so far so good)
- BUT the PC does not become quiet apparantly.
- Pushing the ON-button has no effect at all.. The screen remains black.  :-?

The only option is to plug out the main power.

[Raptor]

What Windows....

[Ardor]

My OS = Windows XP PRO sp2

[unlovedwarrior]

when did this start happening?? what did you do before this started happening?? any new software updates? what protections do you have?

[Ardor]

- It's hard to tell exactly when this problem started. I don't use the standby function every day.
Very recently I 've migrated from NIS2006 towards AVG free anti-virus + Zonealarm.
And I've upgraded my ATI Radeon X800 drivers to a new version.
I've replaced a DVD-player ( from ASUS towards a Sony)

- Other installed protection: Windows Defender.