You won't need to reformat. I can walk you through a Repair Install to fix your problems and keep your programs and data on the computer. You will want to back up the computer before doing so just in case things do not go smoothly with the repair, but it should be fine since the system is stable. It is just the registry that is a mess at the moment.

Many of us on the forums actually do not do not recommend automated optimization tools for Windows 7. Windows 7 does a much better job of handling its own optimization than its predecessors did. We especially do not recommend registry cleaning as an "optimization" step because automated registry cleaning causes more harm to the registry than it actually repairs.

In the future, if you need help optimizing Windows 7, please post a thread in Performance & Maintenance - Windows 7 Forums or follow the tutorial enclosed in that forum to Optimize Windows 7.