The Same thing happend here. The Adobe web page indicates in the troubleshooter that does not always work. the ActiveX instant installer does not work right. I tested for Browser security and ActiveX filtration, and that did not solve it, for me.
The links at the troubleshooter for the Manuel install are incorrect (or aged).
I am not the only one who discovered this. http://forums.adobe.com/message/3961077#3961077 (Forum: why are the direct links not updated.)
At this link below, is the manuel install for flash, "download and self-install" type. It is for deployers and developers , so I avoided it at first myself. It may require Admin install, or elevated (RunAS admin) I do not know.
The 64Bit installer installs both the 32Bit and the 64Bit, I used the EXE installer version myself.
The Browser and the flash control items should be closed prior to installing.
If you get a Green screen or a crash at Youtube specifically (does not happen at all flash video sites). Right Click the player, and get into the Settings, and turn off "hardware accelerated video". . . For me and others, it was an ATI/AMD card, but I am not sure if it is ATI specific yet, or is due to Youtube ADDs. No persons that I read about, fixed the hardware acceleration problem, by changing to a different version of video drivers.
ADDED: hmmm, seems that the "green flash of death", is not as hardware related as they suspected. I just achieved a clean flash install that works perfect , when the other install had that bug? strangeness.
Also In the "flash installer troubleshooter" is info about removing the old flash first, that is related here, but not likely the cause of the instant install failure. I was able to lap install a 10 version with the 11 version. Uninstall should be simple though, in the Programs and features uninstall program.
If somehow uninstall does not work, on thier site they have an uninstaller, I did not test that yet.