Help! Laptop stuck at welcome

Hi - thanks for reading. I'm deperate. I know very little but this forum helped me before.

A couple of months ago my desktop internet died so I started using my daughter's Compaq Presario laptop. It is several years old but was sufficient for surfing the internet, email, etc. I only loaded a couple of programs on it, including AVG and used it minimally. It started doing this thing where you could power it on but it would basically keep restarting. My brother says (& I hope these are the right words) that a sector is bad. He says I need a new hard drive which I ordered but haven't had him put in yet. I sort of put that on hold and started using my son's Dell laptop which he just got in April.

More bad news - I turned the Dell on yesterday and it gets stuck at welcome. You can turn it on and log in but then it just stays at welcome. I tried just turning it off and then when you get the message that the computer wasn't shut down properly I chose to start in safe mode but then it gets stuck checking drives.

Please, does anyone have any idea what is going on and what I can do about it? Thank you so much!