Well here it goes I hope this helps I've been to tons of site looking for an answer on this problem so here it goes. It started off early my WINDOWS XP Compaq Presario system was running fine up until Christmas where it got taken over by a virus long story short had to recover my machine with all my games and in GENERAL files being wiped from the system. Also at that time I installed RAM to upgrade my computer to 2.5gb of RAM around Christmas too, I have a NVIDIA Geoforce fx 5500 video card. The computer runs fine with ANYTHING but a game. I USE Panda, Super-Antispyware, and Eusing Registry Cleaner weekly so I don't think it could be a virus. Anyways continuing on I decided to play Portal/Garrysmod on Steam that day and it comes up with the usual box saying Garrysmod/Portal is loading {Still the game hasn't taken any effect YET} and then it goes to a black screen with the only thing on it is a teal blue square saying "Frequency Out of Range". From there I do not have to shut it down all I have to do is bring up the task manager using {Ctrl-Alt-Delete} and from there I can see again and shut down the game which it says is running smoothly. If anyone can help with this problem it would be most appreciated. 

[recovering disk space - old attachment deleted by admin]Check the resolution and refresh rates on your monitor.