Sudden loss of free disk space

My PC is suddenly losing gigabytes of storage.
The first time this happened was about a week ago.
I had 12 GB of free space, then suddenly lost 7 GB without downloading anything. I ran a full scan with AVG Free Edition, which flagged six threats and removed them.
Immediately after that, the 7 GB returned, bringing me back to 12 GB.
A few days later, another 6 or 7 GB vanished. This time, I scanned the entire computer and found zero threats; the system reported everything was secure. However, the missing gigabytes did not return, and the situation remains unchanged.
It is worth noting that just before this second loss of space, I connected my iPhone to the PC via USB. The storage dropped right after that, so I am unsure if it is a coincidence or linked to the phone.
I cannot recall if I had connected my phone prior to the first instance of lost space.
Any assistance would be appreciated.
Regards,

Maybe try heading into System Restore and deleting that specific point—it might help. You could also grab CCleaner to clear out all that accumulated junk sitting on your drive.

Which specific point should I delete, and what is the actual purpose behind doing so?
I just booted up my PC two minutes ago and saw only 7 GB available. Then, within a minute or two, 12 GB suddenly reappeared out of nowhere without me touching a single thing. It is highly probable this will happen again, so I need to know why this is occurring.
I must point out that following your advice to install CCleaner and clear my entire browsing history after every session did absolutely nothing to help.

Just try doing what they show in this video, and everything should get sorted out for you.

Justin Phillips15 said:Just try doing what they show in this video and everything will be fixed.

Could you maybe walk me through how exactly that’s supposed to help him?

http://windows.microsoft.com/en-us/windows/system-restore

If his settings allow System Restore to use something like 100GB, it’ll just keep filling up and emptying constantly. If you cap it at 10GB instead, it won't exceed that limit. Just look up what System Restore actually does on Google.

Can you point me toward a YouTube video or something similar regarding this for Windows 8? I don't recall having this issue previously, though I can't say for certain. If there's no risk involved, I'll give it a shot.
Where exactly in the settings can I check my current system restore limit?

Justin Phillips15 said:http://windows.microsoft.com/en-us/windows/system-restore

It’s possible he just has his settings cranked up—like if he told the system to let System Restore hog 100GB of space. It constantly fills up and clears itself out, so you just cap it at, say, 10GB. Then it won't go over that limit. Just Google what System Restore actually does.

Fair point, but he mentioned that after his antivirus wiped out some junk files, his storage space came back. That means it isn't a System Restore issue.
Sure, System Restore uses some space, but honestly, that's a good thing. You want that buffer in case some malware decides to wreck everything and you need a way to roll back the clock.
That's a different story from those actual junk files just eating up his drive.

Besides, how can you even know how much space he's allocated to System Restore just by reading his post?

Where can I check my system restore point settings?

Look, man, I get the feeling you aren't really looking to put in the effort here—but honestly, it doesn't matter which version of Windows you're running. Just click that YouTube link I shared; everything you need to know is laid out right there.

Here is what I found:
I clicked on "turn on system protection,"
under disk space usage, current usage is at 570.30 MB,
with max usage set at 0% (974.58 MB).
I haven't followed the steps to hit delete like in that YouTube video yet. I wanted to ask you all first if this is even necessary, because I don't want to mess anything up by mistake.
Is this actually an issue, or should I go ahead and click delete?

George Smith4 said:here's what I found:
I clicked on "turn on system protection,"
under disk space usage—current usage is 570.30 MB
-max usage is 0% (974.58 MB)
I didn't go ahead and hit delete like they showed in that YouTube clip because I wanted to check with you guys first. I didn't want to mess anything up by mistake.
Is this actually the problem, or should I just leave it alone and skip the delete step?

It’s telling you exactly how much is being used right now. That's 570 MB, or about 0.57 GB.
That is way, way less than the 7 GB you mentioned in your first post. Something else is eating up your storage.

It would be a good idea to figure out what's actually hogging all that space first.
Personally, if I were you, I wouldn't touch that 0.57 GB (or even the 0.98 GB max limit) unless you're absolutely desperate for an extra half-gig.

Everything seems fine for now. I’m not actually missing 7 GB; as I mentioned earlier, this fluctuates—it disappears and then reappears periodically.
CCleaner recovered about 600 MB. I have no idea what else to try to figure out why this keeps happening since I'm not downloading anything. What exactly is the purpose of that recovery option in My Computer?

George Smith4 said:Everything seems fine now, so I don't actually miss that 7 GB. Like I mentioned before, this just happens randomly—it disappears, then pops back up, then goes away again...
CCleaner managed to claw back about 600 MB, but I'm stuck on what else I can even try to figure out why this keeps happening. I'm not even downloading anything. Also, what exactly does that recovery option in My Computer do?

You're being a bit vague here. If you aren't talking about something else—since it's hard to tell from your post—that "recovery" thing is likely a recovery partition. It holds the system image or installation files from when you first bought the machine.
Basically, if everything goes south and your OS totally crashes, you use that to roll the PC back to its factory settings.

Whatever you do, don't delete it or start messing around with it.

As long as my data usage is being credited back correctly, I have no intention of touching a single thing.
Regarding any potential new complications, I will update this thread accordingly.
Regards