Bootmgr is missing...?

I hav 2 HDD in my computer( SATA 80 GB and PATA 80 GB). I had win 7 in SATA and now I installed win xp in PATA. Win xp starts up without a problem but when i choose my computer to boot from PATA (which still has win 7), it says bootmgr is missing. Now, how do I run Win 7? I don't hav a Win 7 cd now. Help me plz...