HD installed with XP in Giga MB,not booting up in...

Question

HD installed with XP in Giga MB based comp (comp No.1),not booting up in the originalP3 (Comp No.2) But another similar original machine's (Comp No.3)HD loaded with 98,when put into this comp (Comp No.2),boots fine. No other drive (CD ROM/floppy,USB drives) available/ works in this comp (comp No..2)
Tell me how to make that XP installed HD to go and work fine with the Comp No.2