Well, take the ram out and try to boot. Does it beep? If yes then put ram back in, and disco the hdd. Try to boot with no hdd. Does it beep or display no hdd?
If you mishandled any of those parts, you may have caused more problems than any dust would have. Did you use an ESD strap
when you handled all of those sensitive components? If the answer is no, you may have introduced static onto the system and fried it!