no video output. fans still running but seems everything else is not

I recently bought a second - hand computer off trademe, an auction site.
It worked well for the 1st few days, then randomly when i was using the computer(e.g. playing a game such as quake 4 or even just playing solitare) the screen would turn black and display entering sleep mode, if i tried turning the monitor off and on it would display no video input. So i asked the guy i bought it off and he said it will only do it once a week max. BUT as i found out its doing it every couple of days. he was offering no refunds so i guess il need to get the problem fixed!
So everytime it happens to do this i get no response from the keyboard or mouse and the tower appears to be inactive except for the increased fan noise. Im lost for ideas at the moment, i dont think its the gfx card as iv got the latest drivers for it and when the screen goes black the computer must shut down, cos no sounds play after the screen turns off.

Il post the specs for my computer.

CPU Speed: 2.01 GHz

Memory: 2 GB

Hard drive: 80 GB

CD / DVD: CD + DVD writer

Monitor: LCD monitor



CPU
Athlon 64 3000+

RAM
2x 1GB Ram (ddr 400)

H/D
Seagate 80gb H/D

M/B
MSI nForce 3 Motherboard
Chipset

* NVIDIA nForce3 250Gb Chipset
- Supports Athlon 64 processor (Socket 754), 800MHz Hypertransport interface.
- Supports, DDR 400/333/266
- Supports external AGP 4X/8X
- Integrated Serial ATA interface: dual channel 4 S-ATA RAID controller and dual channel
ATA 133/100/66/33 master mode EIDE controller.

Slots
* One AGP (Accelerated Graphics Port) 1.5V 4X/8X slot
* Five 32-bit v2.3 Master PCI bus slots (support 3.3v/5v PCI bus interface).

On-Board Peripherals include:
- 1 floppy port supports 1 FDD with 360K, 720K, 1.2M, 1.44M and 2.88Mbytes
- 1 serial port
- 1 parallel port supports SPP/EPP/ECP mode
- 6 audio ports
- 8 USB 2.0 ports (Rear x 4 / Front x 4)
- 1 RJ45 LAN jack
- 3 IEEE 1394 connectors (Rear x 1/ Front x 2)

GRAPHICS CARD
ATI Radeon x1950 Pro 512mb

DVD/CD ROMS
LG 52x Dvd Rom Cd Writer
Samsung 16x DVD Writer

FLOPPY
Floppy Drive

PSU
Task 520W PSU

MODEM
Smartlink 56k Modem

PERIPHERIALS
3 12mm COOLING Fans





Please help any input would be greatly appreciated.
Regards Sam

 

Thanks for the reply. um il download it when i get home from school and post back in detail the temperatures.

 

sorry for the long time replying. Um i downloaded speed fan because it was free and the temperatures were if anything low. I reinstalled xp and put a new psu in which didn't help.

Today i downloaded the newest bios drivers which i will get installed over the weekend. A friend was the one who put me onto this and hes good with computers. But anymore suggestions would be great.