Vista Ultimate problem with monitor and aplication?

Hello to everyone,

I install Windows Vista Ultimate 32bit to my PC. Everything was working
fine after this :

1. Every time I install new application, my monitor screen (LCD Samsung
931BF) get darker. After uninstall it's back to normal. Sometimes I must use
restore point to back to normal.

2. When I install some game, fist time I run that game normaly, second time
after restart my pc I get message that problem has been with exe file and it
need to contact for the solution.

I try to disable UAC, but this didn't work for me.
One more problem is that sometimes tell me that I'm not adminstartor of this
pc.
Only I use this pc and my account is set to be adminstrator.

My pc configuration is:

Asus P5W DH Deluxe
Core 2 Duo 6400
1GB DDR2 667Mhz
Ati X1900XT 512 MB DDR3
250 GB HDD

Please Help,
Redmond