Lots of good suggestions from KJT. The key for Boot Options on a Dell is F12.

Toots,
You didn't tell us what failed on the old computer. Was it the hard drive, the power supply, motherboard or something else? Did you have it looked at by someone familiar with computer repair?

I really think you are in over your head. I recommend that you find a local computer repair shop or independent technician to help you. Ask friends and relatives for referrals. Take the "new" computer and the hard drive from the old one and let someone with experience do the work for you.