Computer running very slowly

Question

My computer is running extremely slowly. It takes at least half an hour to boot when I turn it on. I have been able to bring up Systems Mechanic and it took a day to defrag. Defragging is done on a routine basis so that shouldn't have been a problem. It scanned and found 3 problems which it fixed, but it's still very slow. When it starts analyzing the system the computer freezes. What can I do?In case you're wondering this is being posted from my son's laptop.