I've used this card before with a different motherboard & it worked perfect. Now when the computer comes on it shows the windows logo & then it goes blank screen. I've installed the drivers. I don't know what it could be. Any help apreciated.
But try getting into Windows using Safe mode: Press F8 before windows starts to load to get the boot options menu.
If you can get into safe mode then you need to fully uninstall any nvidia or ATI/AMD graphics drivers that are present. Use the uninstall utility. You might also want to run Driver Sweeper (free download that will fully remove graphics drivers). Reboot normally and see if you get in. If you do then install the proper legacy drivers for your OS for that card and you should be good.
Did you change your motherboard on the same install of Windows?
Win XP Pro If I run Driver Sweeper will it remove my onboard graphics drivers as well?
Don't let Driver Sweeper delete any "chipset" drivers as these are needed by your motherboard. But everything under graphics drivers should probably go. In the event that it does kill your integrated driver, you can just reinstall it. Windows can always boot using its built-in legacy driver.
My friend had a similar issue with his PC. When the monitor was plugged into the video card (a PCI based Radeon x1300) , he could see the BIOS splashscreen and could load the BIOS, but as soon as windows was loaded, the screen went black. However, we discovered that we could switch the monitor cable over to the IGP now, and see the OS running... you could also do the process in reverse (plugged into the IGP you couldn't see the BIOS, but could see windows). We ended up fixing it by disabling the IGP in windows and the BIOS, because for some reason when we disabled it in the BIOS XP didn't seem to notice... first off, try switching your monitor to the IGP (I'm assuming you have an igp) once the screen goes blank. Then, under devise manager, disable /uninstall the IGP. Make sure devise manager shows your video card though, probably with some error sign near it. I could be completely off base though, if you don't get an image switching to the IGP I don't know what to tell you, other than to make sure you have the right video card enabled in the BIOS.