Why is my dell optiplex GX260 CPU fan is very fast ?

tell me in detail

Different animal altogether...

Dell site offers Vista. You may get it run in compatibility mode.

http://www.dell.com/support/drivers/us/en/19/Product/dimension-5150x

You say the power light is orange--I'm assuming that you mean the monitor.
This indicates the monitor is not receiving a signal from the computer.
Assuming that the computer actually powers up (fan runs, you can hear the hard drive being accessed, etc) then your problem lies in the video card.

If, on startup, you do see the BIOS info and maybe even the Windows splash screen before your monitor goes dark, then the problem lies in the video card drivers. In this case, starting in safe mode will work and allow you to download and install new drivers.

These things are notorious for having the CPU heatsink grease dry up (and the processor speed steps down) but I'd also scan the hard disk for bad sectors.
If the fan has started sounding like a jet engine, it's more likely that it needs new heatsink grease on the CPU.

Hi there!
The fastest AGP video card that you can get for this computer is an ATI RAGE ultra 128 or an ATI 7500w/TV out.
Hope this helps!

You will need to purchase a wireless router.



Remote Computer Help Fast!

Here you go:
http://support.dell.com/support/edocs/systems/opsx260/en/ug/cvrop.htm#1136140

For other options :
http://support.dell.com/support/edocs/systems/opsx260/en/ug/index.htm

You have 500mA on usb port. If you cause a short on usb connectors, this can damage the motherboard.
Disconnect usb port on motherboard (work with power unplugged ), remove all ide and floppy cable,eventually remove and put back in place bios battery and Ram.
Restart Motherboard only with 1 module Ram (bios battery back in place), CPU and Fan (ensure cpu and fan are well in place), do not plug anything else than switch on button.
If it still does not work there is a good chance you blew the Motherboard.

Regards

Ricardo, here is your driver:
http://support.dell.com/support/topics/global.aspx/support/downloads/en/downloads_splash?c=us&l=en&s=gen&~mode=popup&file=58953