Firstly- if this problem started 1-2 years ago (and it was used for a while before that), then it could have been 3 or more years since the system was last installed. If that was my computer I would do a reinstall anyway. If the toilet's dirty, do you squirt some bleach in there then flush it, or spend many painful hours trying to clean it with a toothbrush? :P I don't get why people think they can easily fix registry problems manually- and I especially don't understand why people trust (and pay money for) a 3rd-party product to go flailing around the registry trying to "optimize" it. Those registry clean-up programs are digital snake oil- they'll never be able to accomplish what a simple reinstall can do, and they also risk introducing new problems.
Seriously though- if you want to keep the existing installation you need to TAKE OWNERSHIP of these registry keys. Forget logging on as administrator. That's the easy answer, and you probably are an administrator anyway.
Right click on the problem keys -> permissions -> advanced -> owner (then add yourself as the owner), then you can give yourself full write access to that key.
The rest is easy- it will work as usual.
I still think you'd be much better off doing a reinstall though! ;)