Hangs when Switching back user

Hey people, I am encounting this problem and I wish to solve it.
I am using Vista Home Premium 32bit.
When i go into my Adminstrator user, and switch to Guest user, it
perfectly fine.
The problem happens when I switch it back to Adminstrator.
There would be a black screen and my cursor when i logged into my
Adminstrator Account.
The cursor would not move and I tried pressing lots of keys but it
doesn't work as well.
The black screen will turn to my background after awhile but my cursor
still doesn't work...The keys are somehow not working as well.

_*Here_are_the_information_of_my_Computer.*_
_Windows_Edition_
Windows Vista Home Premium 32bit
Service Pack 1
_System_
Manufacturer: Acer
Model: Aspire 5920G
Processor: Intel(R) Core(TM)2 Duo CPU T7500 @ 2.20GHz 2.20GHz
Memory (RAM): 4:00GB
System type: 32-bit Operating System


I would like to thanks all at advance =)


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Shawn Tay