Well I am wondering which one of the 3 Performance II series cases you have.
What I always do is make sure to put all the screws in. I mean screws in the hardware that is, a floppy drive has 4 screws so put in 4 screws etc, etc.....
Make sure to have good air flow through the case. I did a search for "Case air flow" on Google and found to many pages to list so you may want to check that out.
Take caution in handling the components when transferring them from one case to the other. They are most at risk while you handle them. Static, dropping, partial dislodging the CPU, etc...
Check all of your connections before starting and make a note as to where they go on the System board, HDD led, reset switch, speaker, USB header, etc. If you have a digital camera you may want to take pictures first, makes a good reference if needed......
Good luck and have fun..... :happy: