System restore is useful in certain circumstances - this isn't one of them. You haven't just installed a piece of software which has buggered up your system. If you had, restoring it to how it was just before you did that would possibly be a good solution.
What you're experiencing here is the inevitable reduction in performance of Windows-based machines over time due to a variety of reasons but, mainly, due to the registry getting filled up with unnecessary junk.
There are registry cleaners out there which will try to fix this for you. They never work properly and, more often than you might imagine, just make things worse!
There's every chance that your machine will be right as ninepence again after it's been trashed and rebuilt. The suggestion of a specialist is a good one - I know how to drive my car but wouldn't have a clue how to do its annual service, so I take it to people who do.
Is it a desktop or a laptop? Does it have a sticker on it with the Windows activation code? It should be a combination of numbers and letters in groups of five, e.g. XXXXX-XXXXX-XXXXX-XXXXX-XXXXX.
What else do you have on there? E.g. what do you use to work with spreadsheets? Is it Microsoft Excel? If so, where did it come from...?