Hi there, and apologies if this question has been raised before. I have had browse through the forums and can't find a thread. I have a 1Tb Crucial M500 SSD as my main boot disk and it was large enough to hold all my data and program files too. I use a standard HDD and external USB for regular data backups. It's been a great product, and until recently was about 400Gb full with 560Gb free space in when checked with Explorer Properties. All of a sudden, Explorer Properties shows 37Gb free and the rest used - yet when I add up all the directories/files, including Hidden, the total usage adds up to about the 400Gb! I have used WinDirStat and it shows a massive "Unknown" file of over 500Gb. This cannot be opened in WinDirStat and of course doesn't appear in the Explorer tree list. I have searched the web for help, and have tried loads of things, with no luck, Indeed, the "bloat" file just seems to be getting bigger! My .edb file is 1.2Gb, Restore is limited to a max of 10% of the C drive, and current usage is 79Gb. PageFile is set at 5Gb. The C drive is 63% defragmented, but my understanding is that SSD's don't need defragging, and indeed it is not actually advisable to do so, so I haven't. I am running Windows 7 Ultimate, with 16Gb RAM. I have checked the BIOS and SATA is set for AHCI and I have "TRIMed" using Acronis True Image. Nothing seems to work and I have run out of ideas?!?! As I have been running it for a couple of years with no apparent problems, I suspect that the problem is due to software misbehaving. I have installed Speed Fix Pro (which creates a restore point with every clean up), Scanguard, SpyHunter, MS Security Essentials and CCleaner, all of which seemed to be working in the past OK. I can only guess that I've picked up a virus form somewhere?? Can any genius shed any light on my problem before I tear out what little hair I have?! Many thanks in advance.