If you have the Dell dvd, use that as Rive0108 says.
If you don't have the dvd, you should be able to boot into the recovery partition by marking it as active.
Rive0108 has provided a partition tool and iso burner - d/l from here:
Dual Boot using free partitioning software
Burn it to cd with the isoburner ( do not format the cd - if autoplay pops up , just close it).
On the non starting pc, Boot from the cd ( at startup watch the black screen with white writing - it will say press F11 or other F number for pop-up boot menu. When it pops up, arrow to cdrom drive , put the cd in , press Enter - it will ask again - press any key to boot from cdrom - press Enter again).
When it has loaded, right click the recovery partition ( should be 6 - 9gb ), and mark as Active . That may be under a rt. click sub menu Advanced.
Remove the cd and Restart.
Hope it helps.