go into control panel> go to the system icon>click on the hardware tab>click on device manager>look under display adapters, is it there,and if it is does it have an error beside it?. if not look for it through the list till you find it.
CPU-Intel Pentium 4 630 3.0Ghz / 2MB Cache ~~OS Windows XP SP2
MOBO-Gigabyte 8I915P Duo Pro Intel Socket 775 (PCI-E)~~HDD-Western Digital 160GB(SATA)
PSU-Aspire 500W ATX~~RAM-1GB PC3200 DDR SDRAM (512x2 Dual Channel)
GPU-MSI GeForce 6600 GT(PCI Express)~~Monitor Viewsonic VA902B 19" 8ms~~ ATI TV Wonder Pro (TV Tuner)
~~Still to come~~: eVGA e-GeForce 7800 GT