I agree with digging up the Windows key, and any other keys you may have lost, even if you don't wipe the system right away. I haven't used a program like that in a while so the one mentioned above is probably a good place to start. Saving a written copy somewhere safe will be important if you have to reinstall for any reason. I've had the issue with hooking up a piece of hardware and Windows saying it isn't genuine. I reinstalled and ommited updates for Genuine Advantage and had no issues. I believe it asked for my key again after the reinstall to 'validate' or whatever. After that it worked ok.
I noticed on a couple machines that worked fine for a while that they had serious issues with performance when using hibernation. over time it would get slower and slower to the point it would take over 4 minutes to recover from hibernate. That was just ridiculous and I ended up turning off hibernate and just shutting down. But there was still some slowdown issues with my computer until I switched to Mint 17 Cinnamon. I really like Cinnamon (using it on my main PC) and would love to recommend it to people wanting to try Linux, but I can't. There is a bug where the screen locks up, and it affects different hardware to varying degrees. On my Core2Duo G41 chipset it almost never has the lockup issue. On this machine (Haswell H81) it happens infrequently but can be really annoying on certain games. On an ASRock J1900 it can lock up bad enough to require a reboot. The mouse moves and usually sound will still be playing but the graphics stop advancing for a while. Usually 4-6 seconds at a time on the Haswell and much longer for the J1900 Bay Trail. This is all with built in graphics. I just got a GT720 and will put that through its paces to see if the problem continues there. The bug is known, but they haven't been able to narrow down the cause and it seems to affect different hardware differently, so it doesn't seem like it will be fixed in the immediate future.
I also agree with trying to transition as opposed to completely jumping ship if you don't have previous experience. I personally would highly advise using a separate machine or a different hard drive to install on. You can just change the boot order in BIOS or hit the hotkey to bring up the boot device selection and pick which OS to use. Unplugging the Windows drive when doing any formatting or partitioning in Linux would also be very smart if you aren't completely certain of what you are doing. I personally haven't tried dual booting from one hard drive, and I really don't think it is the best option for new users unless it is the only option you have. Multiple backups of irreplacable data is always advisable for anyone using any computer.
A tip for firefox - if you don't already have it set up to allow you to save tabs, you can go to about:config, agree to the warning, and scroll down to browser.showQuitWarning, then change to true. This brings up a menu asking if you want to quit, cancel, or save & quit when you try to close the browser. I always use save & quit so I can keep a few tabs open that I want to revisit in the near future but don't want to bother with at the moment. It is also handy if you need to reboot for any reason, or if you have been using the browser a lot and a memory leak is eating your RAM. I sometimes do this with videos I want to watch later, simply click the video, move to a new tab, then save & quit. I can reopen Firefox and it doesn't load the tab until you click on it (assuming you haven't changed this setting). If you have multiple windows open (or downloads, history, or other settings windows), you want to close the window you want to save last.