Windows 7: Losing hard drive space after reboot

Hello. Recently I've been losing large amounts of hard drive space on my Asus laptop upon reboot. It is running Windows 7 Home 64bit. The hard drive is not partioned. It is the OEM hard drive and is about two years old.

For example last night I had about 21 GB free (out of total C: space of ~400 GB). This morning upon rebooting, I had a low memory warning and hard drive space had dropped to about 7MB! This has happened before -- I've moved files to an external drive freeing up several GB and again total space on C: drops to about 10MB after reboot. At the same time this has been occurring, I have also been receiving this error message at almost every boot:
Windows created a temporary paging file on your computer because of a problem that occured with your paging file configuration when you started your computer. The total paging file size for all disk drives may be somewhat larger than the size you specified

Could these two things be related? I don't have access to the laptop currently, so unfortunately I won't be able to provide any screenshots or run diagnostics until later. I also plan to go through Brink's "Hard Disk Space -- How to Free Up and Recover" post. I am curious to hear whether anyone has come across this before. I am concerned that the hard drive may be failing. Thank you in advance.

Check with WinDirStat what's eating your space. WinDirStat - Windows Directory Statistics

If that does not show anything unsusual, run this command in elevated cmd:

vssadmin list shadowstorage

How big is the Assigned number ??

Welcome to th 7 Forum geralph.
I have no idea how you can loose 20 GB of hard drive space just by rebooting. I do know that Windows 7 needs a little working space on the hard drive to work properly.
When it sees that the space is limited it will give you warnings and that is good. Using my 3 brain cells of memory I'm thinking Windows likes about 10% of the hard drive for working room. Removing things off of the hard drive or installing a bigger hard drive is two ways of solving this problem. If it was my computer I would remove things from the hard drive. Take a read through this and you will find other things that can help.
Optimize Windows 7

A infection can be using up your hard drive space without you knowing it unless you do some scans. Using a utorrant can also use hard drive space and get you infected.
I would do some scans with these before you move anything to another storage device. Moving things before the system is clean just infects the other storage device.
ESET
Free Online Virus Scanner | ESET
Windows Defender Off Line
Windows Defender Offline
To put things in order.
1. Scan your computer for infections when clean
2. Remove things from hard drive
3. Go through the Tutorial Optimize Windows 7.
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Please note: If a infection is found all the things your have already transfered to the external storage will be infected also.

Sorry whs I was typing while you were posting. I will get out of the way.

Hi Jack, why would you 'get out of the way'. You added some different and useful ideas that might help. At this stage we really don't know what the OPs problem is. So we have to use the shotgun approach anyhow.

Sometimes I give to many suggestion at one time for the OP comfort level.
vssadmin list shadowstorage is a excellent suggestion. It might be very large.

Thank you VERY much, I will try these when I get home! Some kind of virus or malware infection was another concern of mine. I will update when I'm able.

After running WinDirStat, I was able to determine that the problem was a Norton 360 backup folder. It had ballooned to 151 GB! Judging by the Norton user forums, several people have experienced this. I'm in the process of trying to get rid of the backup set and disable the backup feature (sad when the most common response by the Symantec forum posters is try disabling it!). I also ran a full system scan and nothing came up, although I'm taking that with a large grain of salt after this Norton experience. Thanks for the assistance!

I am glad you could sort it out. Yes, Norton has it's quirks and takes a long time to really master. But it is an excellent AV product. I pick one up whenever I can get it for free.