Aero deactivates when more then 3 monitors are being run off a single GPU card - I've tried essentially everything reasonable to fix it (restore Aero effects to the desktop), but I have come to conclude that the issue is NOT:
1. Driver related (I have tried Windows and various iterations of AMD's drivers (I have a HD6990 GPU).
2. GPU memory related - my GPU has 2GB of memory running for both cores - even though I'm running a LARGE surface area of pixels with 4 monitors, this is within spec for the card, and regardless, shouldn't stress it at all. Other graphics intensive applications run fine.
3. CPU related - my CPU is clocked to 3.3GHz Core i7 975EE.
4. Program related - I've run clean installs of Windows and replicated the effects of Aero deactivating.
Recently I discovered that this is actually fairly common:
One user I believe correctly identifies the problem - Windows constricts Aero to a certain amount of video memory by default; when it trips this amount of memory (say by running 4 large monitors) it simply turns Aero off, regardless of the amount of video memory available. (I was originally going to try to run another GPU, but according to people in the forum, this wasn't correcting the issue, pointing to a Win7 issue)
Whether or not this can be modified (some regedits are listed in the forums above), is unclear. Also, some users report Aero malfunctioning for other reasons which are acutely fixed.
As it stands, I have come to accept that this is a fundamental flaw of Windows 7 when it comes to multiple monitors (None of the OSes in my exp. really support multi-monitor as well as they should given its commonality these days).
For those experiencing the issue, but annoyed by the lack of Win7 'chrome' in the GUI - perhaps Rainmeter, the custom desktop app, might alleviate your need for things transparent and shiny...
So, while this isn't a solution per se, it is a conclusion that I think it's pointless to try to fix this.
well I would think that theory is right, since Aero uses direct 3D. And your right it may have a memory constraint, when it comes to monitor spanning. Still its a small price to pay if the rest of the system works ok, if a bit annoying.
Admittedly, I find it a bit odd why Windows 7, which is (in theory) supposedly more enterprise friendly than the other OSes isn't better tuned for monitor spanning, as obviously most enterprises these days run default multiple monitors stations even for front office staff.
Then again, this is perhaps a niche problem since most people don't run 3-5 large format displays at high resolution.
As an interesting addendum to my summary of the countless forums I read - the suggestion of a user to try Rainmeter, for example, for desktop GUI chrome - is that Rainmeter apparently isn't really designed for multimonitor either; it seems it has quite a few issues when dealing with that spanning.
I'll experiment some more when time allows, and post here for posterity...
I have posted on this issue above, as I've found that Win7 Aero functionality disables after 3-4 large monitors are running; something apparently about the video memory allocation, regardless of GPU ability.
I'm wondering about that now though, as I've seen pictures of many multi-monitor configurations on the web where people seem to still be running Aero, leading me to believe perhaps I'm doing something wrong - does anyone run more than 3 monitors, and still use the Aero chrome successfully?
I have FINALLY solved this problem! (Loss of Aero effects with 4 monitors being used).
As others warned me - apparently there is a video buffer of some sort that Windows enforces for each video card (something like that), and when too many pixels are being rendered, it trips the buffer and disables aero believing that the GPU can't handle it.
So while I use 4 monitors, the aero effects (I understand they're not at all necessary, and some people dislike them regardless), were disabled.
I have since ADDED a second low end GPU (my main card is a dual-gpu card, but apparently that didn't help, or it was a problem because I have 3 30'' monitors and 1 24'' monitor) to power one of the 30'' monitors.
When I reactivated the Aero desktop, it worked!!! Overall, I notice much better system responsiveness as well, as I think taking the rendering pressure of 4 large format monitors off the single GPU (no matter how powerful) did a LOT of good!
I highly recommend adding a second GPU if you want to run LOTS of huge monitors, and I can demonstrate it fixes the Aero problem.