It depends on what o/s your using firstly. If using XP if you change your whole pc it will probably think it has been copied so it will not work, as you can only change so many bits of hard ware in a certain time window.
Secondly if you are using new hardware you will need new drivers but will still have all the old ones on your system.
I personally woul dput all you important data on a few cd-rs and then do a fresh install with all the new drivers to make life very easy.
If not, right click on MY computer and go into properties. Go into device manager and delete all the sound and graphics card/ display drivers. Right click on each one and delete them.
ALso the monitor and IDE ata/atapi drivers. also the computer processor and modem etc. then shut the pc down
then when you plug it into your new pc and start up it will look for all the new drivers.