if a computer crashes, can data be salvaged and how?

Data can often be recovered, but it can be expensive. You can usually recover data from a disk, even if it's not working, but it needs a specialist to examine the disk and extract the data with special equipment. This is usually priced beyond what the average person is willing to pay.

A far cheaper solution is to have a proper backup strategy in place, so that if you lose your data you can recover it from the backup.

Ya depends