Memory disappearing on its own from my C: drive....malware?????

Welcome to Major Geeks!

First just and FYI for you. It is not "memory" space it is hard disk drive space or storage space. Memory is RAM ( Random Access Memory ) which the programs on your PC use to run. Any information in RAM is lost when you turn your PC off. You are probably not losing disk space due to malware. You are probably just noticing loss of space due to System Restore points being created each time you boot your PC. You should consider reducing the amount of disk space being used for System Restore. You can work issues like this in the Software Forum or you can read things like the below:

http://vistasupport.mvps.org/decrease_storage_space-allocated_to_system_restore.htm

I due see some questionable items in your ComboFix log that are not related to your disk space problems, but I need the log from MGtools that was requested before I can continue.

 

Your logs are in pretty good shape. I just have one thing for you to do and then final steps.

Copy the bold text below to notepad. Save it as fixme.reg to your desktop. Be sure the "Save as" type is set to "all files" Once you have saved it double click it and allow it to merge with the registry.

Make sure that you tell me if you receive a success message about adding the above
to the registry. If you do not get a success message, it definitely did not work.
And delete the below file if it exists:
C:\Windows\Knight.exe

Also look for this knight.exe file on any other hard disk partitions or removal drives and delete it if found.

If you are not having any other malware problems, it is time to do our final steps:

1. We recommed you keep SUPERAntiSpyware and Malwarebytes Anti-Malware for scanning/removal of malware. Unless you purchase them, they provide no protection. They do not use any significant amount of resources ( except a little disk space ) until you run a scan.
3. If we had you use ComboFix, uninstall ComboFix (This uninstall will only work as written if you installed ComboFix on your Desktop like we requested.)
   • Click START then RUN and enter the below into the run box and then click OK. Note the quotes are required
   • "%userprofile%\Desktop\combofix" /u
     • Notes: The space between the combofix" and the /u, it must be there.
     • This will uninstall ComboFix and also reset hidden files and folders settings back to Windows defaults.
   • Delete the C:\combofix folder from combofix (if it exists)
4. Any other miscellaneous tools we may have had you install or download can be uninstalled and deleted.
5. If we had you download any registry patches like fixme.reg or fixWLK.reg (or any others), you can delete these files now.
6. If running Vista, it is time to make sure you have reenabled UAC by double clicking on the C:\MGtools\enableUAC.reg file and allowing it to be added to the registry.
7. Go to add/remove programs and uninstall HijackThis.
8. You can delete the C:\MGtools folder and the C:\MGtools.exe file. You can also delete the C:\MGlogs.zip
9. If you are running Vista, Windows XP or Windows ME, do the below:
   • Refer to the cleaning steps in the READ ME for your Window version and see the steps to Disable System Restore which will flush your Restore Points.
   • Then reboot and Enable System Restore to create a new clean Restore Point.
10. After doing the above, you should work thru the below link:
    • How to Protect yourself from malware!