If your system crashes, and comes back up okay, then there is usually nothing more that needs to be done. If, however, your system crashes, and does not come back up, what do you do?
First, you need to be very careful at this point, or you risk losing your data. Depending on what the problem is there are several avenues that can be tried to bring the system back to life, These are tried in order from least likely to lose data, to most likely to lose data.
Many times, it is simply a matter of replacing a corrupt driver, or cleaning up a disk. Sometimes it is necessary to restore from your latest backup, in which case you may lose anything that you have done since that backup was made. This is the reason for doing frequent backups.
The difficult part of recovering a crashed system, is knowing what to try, and what not to try. You can very easily make the situation worse, by running the wrong utility.
The bottom line is, unless you are very familiar and knowledgeable about how your system is configured, what hardware and software you have, and have a thorough understanding of computer crash recovery, the best thing that you can do is nothing. Do not try to resurrect it yourself, but call in professionals. CCS is always ready to help.