Lost Photos - Missing My Pictures Folder

This morning I wanted to make a back up cd of my documents and I burned it. After, I went into Picasa, where I HAD thousands of photos. Nearly all are gone! The "My Pictures" folder is also gone from "My Documents" on the hard drive, as is all the folders I had in "My Documents." The files seem to be on the cd, but I am not sure they are all there. WHY oh, WHY would the files and photos be GONE from my hard drive? How could just making a cd cause the files to disappear? I can't tell you what a tragedy this is! I had thousands of photos that I had edited and projects I had created. Dates that were with photos are gone, since all the dates now show today's date since that is when I burned the cd. As a possible troubleshooting thought--twice I have tried to start my computer and it has frozen at the "windows is starting up" screen, not even getting to the place where I put my password as an authorized user. Please help. I did try a restart and nothing had changed.