New Monitor sleeps at lauching games HELP!

Okay so, this computer is literally brand new, less than a month, and it replaced the old 5 year computer/ But for some reasons, the games that works on that computer, new or old from warcraft 3 to fallout 3 does not seem to work on this brand new one. Everytime i launch a game that goes into full screen mode theres like a 66% chance the monitor will just go into Power Saving Mode and rebooting the computer seems to be the only way out. Why is that? I know the video card is better than the old computer for sure... here are the specs.

Operating System: Windows Vista? Home Premium (6.0, Build 6001) Service Pack 1 (6001.vistasp1_ldr.090302-1506)
System Manufacturer: Dell Inc.
System Model: Dell XPS430
BIOS: Phoenix ROM BIOS PLUS Version 1.10 A00
Processor: Intel(R) Core(TM)2 Quad CPU Q8300 @ 2.50GHz (4 CPUs), ~2.5GHz
Memory: 6078MB RAM
Page File: 1820MB used, 10506MB available
DirectX Version: DirectX 10

Card name: ATI Radeon HD 3650
Manufacturer: ATI Technologies Inc.
Chip type: ATI Radeon Graphics Processor (0x9598)
DAC type: Internal DAC(400MHz)
Display Memory: 3032 MB
Dedicated Memory: 249 MB
Shared Memory: 2782 MB
Current Mode: 1920 x 1080 (32 bit) (60Hz)
Monitor: Generic PnP Monitor
Driver Name: atidxx32,atidxx64.dll,atiumdag,atiumdva,atiumd64.dll,atiumd6a.dat,atitmm64.dll
Driver Version: 7.15.0010.0111 (English)
DDI Version: 10.1
Driver Date/Size: 5/20/2008 23:09:58, 1533440 bytes
WHQL Logo'd: Yes
WHQL Date Stamp:
Video Accel: ModeMPEG2_A ModeMPEG2_C



Thanks!