I cannot start in ms dos mode I have a windows disc in the drive

I tried to install windows me on a older laptop I wiped the hard drive and tried to reinstall but I had the wrong disk so I stopped shut it off and came back later with the right disk but mow I cannot get to the same prompts I could ealier with no OS on this computer I do not know how to start in dos mode or just get the laptop to setup with this disk please help me get back to the screen where I can put the prompts I used the first time I hit escape and “tell” the computer to use the disk in the cd rom but it says it is invalid pleases help