.sudenly Data Lost From System.how To Restore It?

I've been collecting raw data night and day for research from a subscribed data provider (Worldscope/Datastream) for nearly 3 weeks. I kept the PC running day and night because I set up the "Request Manager" for data query. Every one or two day, I saved the batches of data downloaded, cleaned the raw data using SAS, and then ran the next query, and so on. Everything had been fine until one day when I came back to the office to do the usual tasks. To my surprise, my PC look very, very much like it's been reinstalled from scratch without saving anything. Symptons that persuade me to conclude this way is:

- No files/folders that I set up on desktop were there

- My settings are all totally different: I used to keep Task Bar on the right, now it's at the bottom. All "Favorites" on Internet Explorer/Firefox/Google Chrome are all gone, nothing there, no favorites, no favorite bars....

- Usually, when I use hotmail, skype, yahoo mail, etc..., I entered username and leave the PC remember it so that I won't have to re-enter username everytime I want to check for mails. Now, when I open hotmail, skype or yahoo, it's all gone just as if somebody reset the internet explorer or something

- Previously, whenever inside WORD/EXCEL I always see files on "Recent Documents", or when clicking on Start Menu, I used to see files on "My Recent Documents". NOW, on that terrible day, there's nothing like that. ALL GONE, it looks just like somebody has reinstalled the PC without letting us know

- Previously, I kept the settings for Internet Explorer, let's say I keep small Google on the top far right corner but removed Google toolbar with many features. Now, Google toolbars with full features are there, just as if somebody reinstalled Internet Explorer and reinstalled Google toolbars with full features without customizing

- All things that often stay on "Recent Documents" or things like that in some applications such as SAS, Stata, etc... are all gone

ONE MORE THING: My university sometimes runs maintenance for all PCs in the School and in the lab. I'm talking about this because perhaps the maintenance automatically reinstalled the whole PC??? I suspect it couldn't???