Well, unless you know the reason your old computer died, it is safe to include that the hard drive could have been the source of your previous computer's problems. There is no guarantee that the older hard drive still functions and data can be retrieved from it, short of sending it out for data recovery, which is often times prohibitively expensive. In your case, however, it sounds like you could write off data recovery services as a business expense.
It is always possible that the formatting or partition information of your older hard drive became damaged in some way, rendering the data as no longer there. The older computer that was using that hard drive as it's primary would of course no longer work if that happened, and the drive would either appear blank, needing to be initialized, or otherwise not show up as a proper functioning drive. If you have important information on the drive, make sure you don't write anything to it or make any changes you aren't sure will fix the problem, as this could result in overwriting anything important that used to be stored on the drive. It may be worth scanning the disk with recovery software to see if perhaps it's as simple as fixing a partition table.