Can't watch PBS, other videos online

Question

It was always possible to watch videos online at PBS and other sites before on the computer at my mother's apartment, but now when I got there, the screen is black, with an error message saying that a plug-in (or plug-ins) is/are blocked. I really don't know what to do about this, and I don't even know which plug-in is involved. I don't want to mess around with the folders in the Library. Several people use the computer, so someone may have changed a setting. I've run Disk Utility, but that did nothing, and my sister, who owns the computer but doesn't live with my mother, couldn't care less about it. My mother loves to be able to see content from PBS and other sites online. Can you help me? I hope that the solution is a simple one.
Many thanks,
jenny

Answer 1

I think you must be right. The problem, of course, is that my sister has forgotten her adminstrator's password and is disinclined to change it to one she can remember. Well, thanks very much. If she comes around, I'll take it from there.