Hammer slowed down to a crawl

[Przemek]

I don't know when did this happen exactly, might be after the latest Steam update - when I launch Hammer, the application is extremely slow and not responsive. It's impossible to do anything, because highlighting a menu or a toolbar button takes 10 seconds! When I tried opening my map throught the File -> Open menu, a progress window showed up saying "Reading chunks" that hangs at 5%.

CPU usage in Task Manager stays at 0% all the time.

I tried using "refresh sdk content", removing sourcesdk and sourcesdk_content directories - no success. Last option is to redownload the whole thing...

I'm using Source SDK with -engine ep1, for I do not have Orange Box on this account.