|"I have installed the Drivers first, but the monitor still does not switch on"|
You should NEVER install the drivers first! But you should have uninstalled the old drivers before installing the new card. Once the new card is recognized, you would have been prompted to install the drivers. Actually, I'm surprised you were able to install the drivers in advance, normally you would get an error message that says something like "no nvidia card was found".
The FX5200 is a low end card that does not require an aux power connection. As the others have mentioned, if you're upgrading from onboard video, you need to enter the BIOS & disable the onboard, then change the "initial Display" to either AGP or PCI, depending on which type of card you have. But regardless of the BIOS setting, you *should* be seeing the POST screen or splash screen when you bootup. Are you at least seeing that? Are you hearing any beeps?