Why does my iMac freeze so often?

Question

I got an iMac computer last May, and ever since then I have been having some issues that can be quite annoying. First of all, it freezes very often. I could be in the middle of reading an email and suddenly the rainbow spinning ball comes on and never seems to go away. Sometimes I go off and do something else just to see how long it would take for my computer to un-freeze, but after being gone for several minutes, it still continues to load. I end up having to restart the computer about 5-6 times a day because of constant freezing. Again, this computer is barely 7 months old and I already have some serious issues. I do not run many apps at the same time, and the only apps that I have running most are Safari and Skype. I don't run any big programs that could slow the computer down, so that can't be the problem. Also, sometimes when I try to use the computer, it is just a black screen. It isn't black like it's turned off. It's kind of hard to explain, but it seems that the computer is on because it emits light, but it is just a black screen. But the problem is that I can't do anything to wake it up. Moving the mouse doesn't work, so I am left to holding the power button down to turn it off. This probably happens about once a day.  I am not sure if this issue is connected, but I might as well mention it anyways. Many apps don't respond and I need to force-quit them quite often. The app that I have the most problems with is iMovie. It seems almost impossible to open it because each time it freezes and doesn't respond. I have this once in a while with Safari, but not nearly as often as iMovie. Sorry for the amount of questions, I have just been kind of disappointed with the problems that I have been having, especially because the computer is not old at all. My family has the exact same computer which is only a month older than mine, and it operates perfectly. The same applications are loaded on both of them, so I don't understand why my computer has so many issues and my family's doesn't.

Answer 1

The next time you have the problem, note the exact time: hour, minute, second.
If you have more than one user account, these instructions must be carried out as an administrator.
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
Make sure the title of the Console window is All Messages. If it isn't, select All Messages from the SYSTEM LOG QUERIES menu on the left. If you don't see that menu, select
View ▹ Show Log List
from the menu bar.
Scroll back in the log to the time you noted above. Select any messages timestamped from then until the end of the episode, or until they start to repeat. Copy them to the Clipboard (command-C). Paste into a reply to this message (command-V).
When posting a log extract, be selective. In most cases, a few dozen lines are more than enough.
Please do not indiscriminately dump thousands of lines from the log into this discussion.
Important: Some private information, such as your name, may appear in the log. Anonymize before posting.