Flash stopped working, can't reinstall

Just yesterday I started having problems with Flash. Every site I went to with Flash on the page stopped responding. I needed to ctrl-alt-del to stop my browser. Going into Manage add-ons and disabling all Adobe plugins fixed the problem, except it obviously prevented me from seeing any Flash-based content.

I uninstalled Shockwave and Flash, then couldn't install Shockwave, and had to find a standalone installer to complete the install. Now I can't install Flash. The Download Manager starts up, doesn't install anything, and then shows me a nice big yellow button that says "Close Download Manager." I've tried deleting the download manager several times, but no luck. I've tried running the standalone Flash installer, but that didn't help either.

I haven't installed any new software or drivers, and have made no other changes to my system that may have triggered this problem.

I'm running 32-bit Win7 (completely up to date) and have tried IE9 and Chrome (both current versions) to no avail.

What a mess.