Keyboard Problem after right clicking

Hello, I'm running FS2004 with WinXP Pro. (ATI X700 256, 1280*800)FS works well, but each time I do a right click and change view or left click elsewhere, FS continues to run, but my keyboard seems to be desactivated, and i cannot neither access to the menu using the Alt key : FS stops, exactly as the menu appears, but nothing more happens.The only way i found to use my keyboard back is to switch to another application via Alt-Tab, and to switch back to FS2004, but it is quite annoying...Any idea for solving this quite strange probleme ?Thanks, sorry for my bad englishPascal