Solved! random pop up unnamed window at the left corner in windows 7

[denizorman.ieu]

I have a problem for 6 months and I do not have any idea what caused it to start.
one small window is appearing randomly in the left corner and stays there around 4-5 seconds and disappearing again. During this time, computer is stucking or slowing down a lot. I am using Avira and it did not find anything. I also formatted computer and installed again. But it happened again. I could not find the solution. I will be a lot appreciated if someone faced with that problem before and can help me then ? I also attached the pictures so you can see how it looks like.

for the screenshot --> https://ibb.co/iJuX5S

 

[hang-the-9]

How soon after a clean Windows setup does it start popping up? Keep track of what was installed on the system vs when this thing starts.

 

[Prostar Computer]

Check your startup items & services in MSCONFIG. Fair chance that it's a legitimate .exe if you just installed Windows and only the drivers, along with your Anti-virus, but if you threw more than that on there, take a look at startup entries.