When installing hardware, there is a potential risk that things will not turn out as planned. Besides the danger of static electricity, you may end up with a new part that doesn't work or causes other components in the computer to fail. In the second worst case, the computer may fail to do anything at all. If this happens to you, here are a few things you can do to correct or at least pinpoint the problem:
First of all, if the computer starts smoking or emitting a burning smell, turn it off immediately! This indicates that something in the system has shorted with the power supply. Rather than try to take care of this problem yourself, it's best to have a professional computer service person take a look at your system. Even if you think you know what caused the problem, it's possible that permanent damage has already been done.
If the computer just sits there spinning its wheels, with no other sign of activity, that means that some of the data circuits in the computer are either shorted or disconnected. In this case, start by undoing what you just did to the computer to try to get it back to where it was working. If the computer still fails to start, then it's time to take things apart. Turn the computer off, then begin by disconnecting all of the external cables from the computer: monitor, keyboard, mouse, printer, etc.; until the only thing left plugged in is the power cord. Then switch the computer back on and see what happens. How can you tell if the computer is working with no monitor? Nearly all computers will sound a single beep after performing their self-test. If there is no beep for several minutes, then you have to dig deeper. The next step is to start disconnecting the cables that are inside the computer (at this point, you may decide to have a service person take over.) Make sure you note where the cables are going before you unplug them, and remember to turn the computer off when working inside the case. If the computer still fails to beep after that, try removing any expansion cards you may have. In the extreme, the only things that need to be left attached are the motherboard, CPU, at least 1MB of memory, and the speaker (so you can hear whether it beeps.)
After you have gotten the computer to the point where it does the self-test and beeps, proceed to reconnect everything you have unplugged, one cable at a time, testing the computer again after each one. If by chance the computer fails again after reconnecting a cable, there are a few possibilities to check: you may have the cable connected improperly or the device attached to the cable may be configured improperly, in which case you should check the owner's manual for that device to see how it should be installed; or the cable or the device may be defective. Leave that cable disconnected for now until you can have a professional take a look at it, and proceed with the remaining cables.
If the computer does its self-test but reports a device failure, check the cable that attaches the device to make sure it is installed correctly, and check the settings for that device to make sure they are correct. If you have just installed a new component and that caused a different device to fail, check the configuration for both devices to see if there is a conflict (again, refer to the owner's manual for configuration settings.)