Well.... the first things you want to do is scan for viruses, check for adware/spyware and do a defrag.
How much space are you using on those hard drives? If you're using most of the one with the OS on it, it can start lagging pretty bad.
Check your running processes and programs. Do you have a lot of background apps that start with the OS? If so, you might want to keep those off until you need them.
Considering you've had this computer for a year, it's quite possible that bits and pieces of programs and files are cluttering up your drive. For example, many programs don't remove all their files when you uninstall them. They might leave user settings in case you decide to reinstall. These little things add up and can bog your computer down. You might want to consider formatting your drives and starting fresh. That's only a suggestion though. There are programs that supposedly clean out all the junk on your computer, but I don't have much experience with any of them. I personally would reformat, but it's up to you. I'm just here to offer options.