Vista - WMC and WMP11 keep crashing

Hi there, I hope someone can help. I'm trying to play avi (divx) files on Windows Media Player 11 but every time I open WMP up it just closes itself. It's the same whether I double click on any media file or try to open up the program first.

I then tried to open the files in Windows Media Center but it crashes as soon as I open a file.

I have Vista Codec Package installed and it had been working flawlessly until yesterday. I discovered that divx files that would previously stream to my Xbox fine were now not working and my Xbox was giving me an unsupported file type message. When I investigated further, the files would only play sound, not video on my pc, yet they'd previously worked fine. I reinstalled the Vista Codec Package and in ffdshow made sure Xvid and divx decoders were enabled. this fixed the problem and I was now able to watch the videos on my pc no problem (although still not able to watch them on my Xbox like before).

However, today I can no longer use WMP11 or WMC. Can anyone help please?

Edit: Since posting this I've tried installing VLC Player but had problems with that too so uninstalled it. Ditto for GOM Player.

UPDATE:

I uninstalled Vista Codec Package (not an easy task, the uninstaller wouldn't work so had to go the registry route- even CCleaner could not remove it).

Windows Media Player still will not open up. Windows Media Center still crashes as soon as I try to look in my libraries.

I've tried to download, install and use Winamp but when I ran it I got this error message:
Problem signature:
Problem Event Name: APPCRASH
Application Name: winamp.exe
Application Version: 5.5.2.1800
Application Timestamp: 478d39f3
Fault Module Name: StackHash_8d13
Fault Module Version: 0.0.0.0
Fault Module Timestamp: 00000000
Exception Code: c0000005
Exception Offset: 4d8b4446
OS Version: 6.0.6000.2.0.0.768.3
Locale ID: 2057
Additional Information 1: 8d13
Additional Information 2: cdca9b1d21d12b77d84f02df48e34311
Additional Information 3: 8d13
Additional Information 4: cdca9b1d21d12b77d84f02df48e34311


I'm totally beyond fed up now, not only can I not get WMP or WMC to work, but I can't get ANY media player to work! I'm tearing my hair out! I just did a reinstall of Vista less than a month ago, I don't want to have to go through that YET again. I'm seriously considering switching to Linux. Even the daunting prospect of using a totally new OS is starting to seem more appealing than continual headaches with Vista.

I don't know if it's relevant or not, I've also discovered Internet Explorer x86 will not open up (I get a very odd windows error message saying "Cannot find http://www.vistax64.com cannot be found. Make sure the path or internet address are correct." IEx64 does work though.