Do you get the same issue if you: 1. perform a clean boot, or 2. create/use a different user account?

By only disabling "Load startup items" in msconfig, the problem has gone. Now I need to find the culprit. What does exactly that check disable? I suppose HKLM/Run and HKCU/Run + Startup menu items.

Yes, that's correct. You can select the Startup tab to check the existing items. Then you can enable just half of them and restart Windows. If you get the same issue, you split the enabled items in half again, and repeat the same process till you find the cause; if you don't, you try the other half and do the same.

Binary search tree? :D

Yeah. log2(x) tries at worst, where x is the amount of startup items. Please report back your findings when you're done :)

Actually, by remembering what I installed recently, I found it at the second guess. It seems to be the Citrix receiver (for remote desktop). I will investigate if it's necessary to leave it in startup.

Found that the Citrix browser plugin works well even without the element in startup.

If you rewrite your comment as an answer, I'll accept it.

@Teejay Well, that was a naive algorithm. Program install date can indeed bring more information to the table ;)

For reference, what's the program version you currently have installed?

It appears to be a bug, which could have been eventually fixed in a newer release.

@Teejay Now that I think about it...

citrix.com/downloads/citrix-receiver/windows.html

It might even be a feature.

Maybe the program disables those effects on purpose.

Yes... probably

Now I tried to launch a citrix application from web browser

and aero effects (which were enabled on startup) are now disabled

Like I guessed, then.

But, If I re-enable them via System properties, then relaunch a citrix session

they remains enables

and it seems to have no issues

What's the exact executable that gets launched?

I disable 3

I see. What are they called?

Citrix receiver (which is in startup)

"C:\Program Files (x86)\Citrix\SelfServicePlugin\SelfService.exe" -showAppPicker

BTW, found a similar question on Microsoft forums: Windows 7 Window Animations Disabled automatically

Yes, It seems to be a long-time bug (or feature)

What if you disable just some of them?

From auto-starting, that is.

I'll try with concentr, they talk about Connection center in your link

Found a (possibly) related question: Windows Aero not working on Zero Client

If I read that right, it might be that certain effects are disabled if you don't meet some requirements.

Some official article: How to Prevent Disabling of Aero Redirection for XenDesktop 5.5

@Teejay This article also seems to confirm what's causing the issue is concentr.exe

The last one did the trick! Thank u! If you want to write it down as an answer, I'll be glad to accept it.