after some years with xp, 7, 8, discovered all take up about 62GB after service packs, updates. that's as big as it got as of not too long ago. xp system requirements are 1.5GB for initial install (did they change the page?).
http://support.microsoft.com/kb/314865
windows 7's system requirements are 16GB of space for initial install.
http://windows.microsoft.com/en-US/windows7/products/system-requirements
you should have at least a 250-500GB drive to use windows minimum. I prefer to have a 2-4TB or larger drive, but the drives over 2TB must be GPT partitioned and require special BIOS configuration to support UEFI boot to install correctly to see the whole drive.
defrag will tell you it needs 15% free space to run (ouch).
restore points only last for 30 days and then get dropped. so it's not that big of a deal, keep your restore points.
what size is your hard disk? what is reported when you bring up my computer?
turn off virtual memory, your system will probably become more stable. I discovered 2 bugs in windows 7 virtual memory on my new box (win7ult64sp1retail). but it won't fix the disk space problem.
with windows 7 I discovered it was writing 2,422,996,992 bytes/day to my (what I thought were) pretty much unused SSD's. SSD's have a rather limited qty of Program/Erase(PE) cycles per block (800 for TLC, 3000-30,000 for MLC, 100,000 for SLC. but I still found out that the drive is going to theoretically last about 13-50 years depending on how many hours in the day you use your computer. I still treat the SSD gingerly as far as writes (I have a samsung TLC), no defragging or full formatting or wipes if I can help it.
hard disk writes don't matter, but they have a lifespan of about 5 years. there is drive closing software available like http://www.fssdev.com/products/casper/ it's the best drive cloning/upgrade software on the market (can be buggy once in a while, so work with tech support on it). compared to the other solutions I have tried, this one works far better. this may be your best solution. buy a drive and a drive dock, and clone your drive while growing it/filling available space. if you choose that option, it won't be same size partition as old drive, it will have more space and make use of the larger space of the new drive.
a good USB drive dock that has a usable fan is
http://www.newegg.com/Product/Product.aspx?Item=N82E16817707260
crank up the fan to max.
do a rootkit scan. mcafee has rootkit detection/fix tools.
http://www.mcafee.com/us/downloads/free-tools/index.aspx
if it's malware, there may be a need for a wipe and reinstall.
do NOT clear out temp files except for possibly .log files, and even then sometimes those are part of installers. the temp directory should be touched by anything. installers tend to get installed there. antivuruses mistakenly think this is a good place to clean things up. but like on *nix, you don't mess with /var/tmp just like on windows you don't mess with windows temp dir. if you are using *nix utilities on windows, you may have a number of temp dirs.
software uses temp files as an interim for making other files, possibly when you save documents. they can also be left around in mass quantities, as in the case of some printer logs.