Please Help. For some reason, I have numerous, numerous problems.

Question

For starters, my macbook is roughly a year old.
For the past, 2-3 months, I've been having some problems.
1. Itunes. Oh, where to start with Itunes? One day I try to open up my Itunes to listen to some music, and I get a message, it says exactly this: "The file 'Itunes Library' does not appear to be a valid Itunes library file. iTunes has attempted recover your iTunes library and renamed this file to "iTunes Library (Damaged) 2". And I discover that all my music has been deleted from iTunes expect for about 10 songs, and neither of them work correctly. So I patiently fixed it (properly or improperly, i have no idea) and it worked, for about 2 weeks. Then I try to open my itunes again, and I get the same message. Today it happened again, for the 5th time. Does anyone know a permanent solution to this problem? This has never happened to me before, except for the last 2 months or so.
2. iPhoto. I had some of photos in there. I try to open it one day and it gives me a welcome sign, as if I just got iPhoto and was using it for the first time ever. Then it says "loading photos". However, I doubt it was actually loading photos, because it shouldn't take 5 hours. I tried the advice that the apple website gave me on this one, (it was something like, hold two keys, a box will come up, press blahblah) but it didn't work.
3. Safari. Everything seems to be working correctly, except for everytime I open Safari, it makes me type in my user password for something called a "keychain login". It has never done this before. It's getting really annoying, everytime I open a webpage, it comes up. When I type in my login and "reset" my keychains, it does the exact same thing as when I click cancel. I honestly have no idea what it means, but it does the same thing for the IM service that I use.
4. TextEdit. I try to open a (quite important) file and it says "File (file name) could not be opened" I have no idea why, and this is the only file that it has done this for.
I believe that to be about it. If anyone has anything that would help, that would be fantastic.
However, please try to be as simple as possible when explaining things? I'm not dumb, I just want to make sure it gets fixed correctly, without screwing it up more.
Thanks in advance!

Answer 1

It's interesting that only Mac application software is involved. I presume you've done a permissions run on Applications/Utilities/Desk Utility.
Back up your data files. Now, if you have your install disks, you can safely perform an Archive and Install, but preserve current users and settings. You'll end up with a fresh system, though you'll probably have to reinstall some third-party software to make it work well. Of course, you'll also have to update the system. This method comes closest to restoring functionality to all the applications you mention.