Vista doesn't turns off my display

From quiet a long time, I’ve been running Vista Ultimate in a Dual Boot configuration with XP Professional on a brand new desktop computer. XP is installed on C partition while Vista is installed on D partition. Partitions E and F are reserved for data files.

Motherboard: ASUS P5N-E SLI
Processors: Intel Core 2 Duo
RAM: 2 GB
Monitor: SONY Flat Panel SDM-HS53
Graphics Card: NVIDIA GeForce 8600GT

My problem:
Vista Ultimate does not respond to the settings for “Screensaver” & “Turn Off The Display” that works in the XP Pro environment.

In both version of Windows, I have Screensaver set to begin 2 minutes after computer inactivity. That works OK in both XP and Vista.

However, whereas the Display shuts off after 15 minutes in XP but NOT in Vista (even though 15 minutes is the “Turn Off The Display” setting). The screensaver slideshow continues even a half hour after inactivity in Vista. I’ve never seen Vista shut down the monitor as long as I’ve used this new computer (a few weeks); the screensaver slideshow is still on even a half an hour after I’ve left the computer idle.

I’ve tried changing Power Plans several times, but nothing “takes” in Vista. What else does one have to do inside Vista to force the operating system to turn off the monitor after 15 minutes of inactivity (like XP Pro is doing without any problems)?

I do NOT want to reinstall Vista from scratch, because I already invested many hours installing various programs in the Vista environment, and tweaking them. All those hours of work would go down the drain if I have to reinstall Vista from scratch.

Is there some other control that has to be activated in Vista for the settings in Power Plans to take effect? Why does the Screensaver function work OK, but NOT the “Turn Off The Display” function?

I am logged in as Administrator in Vista when adjusting all these settings.

I’ve read all the related HELP files that came with Vista related to these functions, but so far I’ve found nothing that helps me solve this problem.

In Advanced Power Settings, I turned “Display / Adaptive Display” to OFF, but that didn’t do anything either. I shifted from Power Plan “Balanced” to Power Plan “Power Saver,” and that didn’t work. I have “Put the computer to sleep” set to NEVER. Is that relevant somehow?

Tks in advance

Go into the power settings and reset everything to default. Reboot and then select the 15mins for the monitor. See if it works.

Thanks for the reply. I tried but it didn't work. The monitor still does not shut down after the specified time has elapsed (when running in Vista mode).