Yeah,,Did that ,,,Doesn't work..
Don't see how an install can be account specific...
When you install some programs you're asked if anyone can use the program or just the user installing it but I don't think that's the case with Flash but thought it might be worth a try. If you haven't done so, you could install Firefox and see if that fixes it, could be an Internet Explorer issue. One of my grandkids is running into a similar problem but with audio, she has audio on her user account but not a second. Last time I talked with her she said she didn't feel like spending time fixing it so don't know how she'll resolve this. I know you said you didn't want to create a new account and transfer everything over but this may be the quickest, easiest way to fix it.