iChat not running at all

Well let's begin from the beginning. I bought an iMac, worked perfectly for awhile. Then iChat started acting up (I couldn't video chat with my friend who was on a Macbook), and I searched for the answer. Found it. Worked for like a week. Then! It decided (after the 10.5.4 update) to completely fail. I mean, the icon changed to this TextEdit looking thing but with a ruler. There is no iChat anything in my Mac anymore. Besides that icon and the name and a problem report which states:

Process: iChat [209]
Path: /Applications/iChat.app/Contents/MacOS/iChat
Identifier: com.apple.iChat
Version: ??? (???)
Build Info: iChat-6080000~1
Code Type: X86 (Native)
Parent Process: launchd [170]

Date/Time: 2008-07-14 14:46:04.203 -0400
OS Version: Mac OS X 10.5.4 (9E17)
Report Version: 6

Exception Type: EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000002, 0x0000000000000000
Crashed Thread: 0

Application Specific Information:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Couldn't load DefaultDefaults'

Thread 0 Crashed:
0 com.apple.CoreFoundation 0x9035aff4 ___TERMINATING_DUE_TO_UNCAUGHT_EXCEPTION___ + 4
1 libobjc.A.dylib 0x951780fb objc_exception_throw + 40
2 com.apple.CoreFoundation 0x9035af2b +[NSException raise:format:arguments:] + 155
3 com.apple.Foundation 0x930b3c95 -[NSAssertionHandler handleFailureInFunction:file:lineNumber:description:] + 101
4 iChatCommonGUI 0x00672653 RegisterDefaults + 232
5 com.apple.iChat 0x0013c100 0x1000 + 1290496
6 com.apple.iChat 0x00003736 0x1000 + 10038


If you need more of the Problem Report, I saved it. So just ask.

This is my first Mac and I really hope I didn't mess it up beyond repair.