There are two schools of thought on that. Some say that it is best to leave the computer on all of the time and not to turn it on and off. The harddrives are always spinning when the computer is on but they say that the harddrives having to turn off and then start up wear out quicker.
The other school of thought says that the computer should be turned off whenever it is not in use because the harddrives running constantly without a break for days and days is what wears them out.
Harddrives are built to last a long time (both spinning continually and being shut on and off). I think that you just got a bad one. I know of computers that run for weeks without being shut off and they have done so for years. I also know of computers that are shut down everytime they are not in use and they have also run for years.
I prefer to hibernate my computer when it is not in use. If you are constantly turning it on and off, I can see where it may be better to leave it on all day but just shutting it off a few times a day should not be a problem.
There is a setting in Control Panel - Power Options that allows the Hard Drives to turn off after a certain amount of inactivity, but I do not recommend using it because it is quite inconvenient to have the harddrive turn off when you are using the computer.