HD 5850 + HP w2408h = monitor will not sleep unless computer stays on

I think that's normal. Have you waited a while longer? The monitor should put itself to sleep again.

nope, it would stay on all night and still be doing it in the morning.

however, i fixed it...in a way that makes no sense. i first reset the monitor to default settings, then manually set a sleep timer. any timer at all works. i set mine to go to sleep at 3am, for example.

now, the monitor functions like it used to: if the computer turns off, the monitor displays "no signal" for 30 seconds, and goes to sleep.

no clue how that solved anything, but there you go.

Mate the same exact thing is happening to me...  

ill try to do what u did and see if it works, i was already considering buying a new monitor  

lets hope it works  

Would you explain further about the 'manually set sleep timer'. I am a novice at this and reading all I can to learn more...having the same problem, need a sleep timer!