Display flashes on and off??

[gklofa]

As I am scrolling around windows, and opening and closing windows, my display will disappear and re-appear. It is not a monitor problem, and when the display re-appears, my mouse will be momentarily not visible, but working, until I click the buttons and do something. My system specs are below. Hope someone can help.
thanks Greg

CPU:- Intel P4 1.5 Ghz External clock 100 mhz

M/Board:-
Gigabyte GA-8SR533 F4 bios version 6
SIS 645 + SIS 961B AGP set
Socket 478 CPU/FSB 533/FSB 400
3 DDR DIMM /ATX
AC97/ATA133
Bios ROM size 256k
Cache size 256 x 1k

Memory:-
512meg 266DDR ram

Graphics:-
Chaintech GeForce 4 MX440 64 meg ddr, using version 40.41 detonator driver

Modem:-
Netcomm – Inmodem S6 – IN5699_3

Sound Card:-
Hercules – Muse 5.1 DVD

HDD:- 1x 40 gig Seagate 7200rpm primary
1x 15 gig Seagate 4200?rpm secondary