Boot off your free UBUNTU CD and look around from another LiveCD no-install boot CD.
I have a Dell Inspiron 531 AMD 64 Dual Core 2.11 GHZ, 160GB HD and am running Windows Vista Home Basic.
My computer tells me now that I only have 6.5 GB of memory left of 148GB (partitioned into 150GB and 10GB for Backup Disk). I have run Disk Clean up and Check Disk (only for scan and recovery of bad sectors).
I used TreeSize to see if I could find any large files and it only accounted for 28GB of the 130GB of used space. Where could my other 100GB have gone??
I have no Quotas set, and no System Restore points set. I can't seem to account for the "files" that are using up my hard disk.