Yes, delete fp.dsk.
I had the same problem over and over, on XP as well as win 7. Drove me nuts. Something goes wrong with fp.dsk, and then the IDE will inevitably crash, e.g. after typing a four character word; another indication that fp.dsk is corrupted is when you compile your code with an error and the IDE reloads your source and displays it in another window with a garbled name such as myprog||.pas... it may even try to save it which then fails because this file does not exist etc - this can become quite a mess.
I issued a bug report on this long ago. It's quite sad as it pisses off newbies and it almost got me steering clear from fpc.
I do not exactly know what is stored in fp.dsk, and all I miss after I've deleted it is the desktop history. But it may be a good idea to store a copy occasionally while you are sure it is still healthy.