Right, so I have a twofer for questions.

My computer has been really sluggish. I've cleaned it (gonna do another as the last was still a fair ENOUGH time away but was relatively recent), made sure I got rid of bloatware, and so on. But it seems to be that its still sluggish. Like, I open up a folder typically or do a search on my computer, and it takes forever. Granted, yes, I've got 244 gigs of 913 free, but it seems super slow and I've been around this number for a LONG while and I don't see why I have so much issues. I also notice my memory and disk usage in task manager is usually high, and disk usage often is at 99 or 100% at times where it doesn't seem like it should be.

Second question. I've been considering reformatting my laptop, as I figure it'd help with some issues and a "system restore" really doesn't seem to help much (anyone care to explain why that is?). Problem is, my laptop came preformatted with windows 8, no disk. It was then upgraded through digital download to 8.1 (through MS store). Now, how could I reinstall my windows if I were to format the laptop? I don't even have an activation KEY or anything (no sticker with it on the laptop). Any idea what I can do?Wait. Do not format your hard drive. You may have other issues.
Do you use a good AV program? If so, which? Do  you scan often? What have yoou found?
What do you mean when you say you 'cleaned' your laptop?
If there is a lot of  free space, there  is no need to remove things.
Have yoou read this?
http://windows.microsoft.com/en-us/windows/improve-computers-performance
Select Windows 8 in that AREA.