What make is the computer?
There are several manfrs - e.g. Compaq / HP, Dell and possibly others - that use proprietary components (e.g. power supplies) that are effectively "unique fit".
If that's the case, you could be stuck - you couldn't simply swap them into a new case.
Also, stating the obvious, ensure that any replacement case has capacity for the number of HDDs, optical drives, etc. that you need to accommodate!
SD