OK I think I have a solution.
A few days after reading your original post, I started having the exact same problem...a week or two after I downloading version 5.23. I couldn't open any of the feeds or any type of file. It would say connecting and just stop when trying to open feeds.
I'd try to delete Winamp to reinstall the same version, but it kept giving me the message that an instance of Winamp is still open...must close first etc etc and gave the abort/retry/ignore options. So I'd ignore, let it uninstall what it could, and try to delete the rest in Windows Explorer. It'd give me the same message, saying Winamp was open and must be closed first. Same thing when I'd try to reinstall. Then I decided to reboot, and when I did, about 10 or so times it did the "closing Winamp" thing before rebooting. So apparently even when I closed the program it never actually closed each time, though it never showed on the system tray.
After rebooting, all instances were obviously closed so I was able to uninstall completely and delete all remaining files.
I then did a google search for "download old versions winamp" and got http://www.oldversion.com/program.php?n=winamp
. I downloaded a random one a few versions back, 5.1, because honestly I can never tell the changes in each one because they don't affect me. It's working just fine.
Maybe there's something corrupt with 5.23 but it only affected some people because of something in particular with their systems. I really don't know enough about this stuff to say.
Either way, it worked and I can listen to feeds again. It was hard not listening, especially right after all the NorCal and N90 feeds came up! Hope this works for ya.