On start up my advent laptop says :
BOOTMGR MISSING CTL-ALT-DEL
I don't have the original discs what do I do

Check this out:

Ideaz - JohnDa's Fundas & Ideas: BOOTMGR is missing, Press Ctrl+Alt+Del to restart (http://johndasfundas.blogspot.com/2009/08/bootmgr-is-missing-press-ctrlaltdel-to.html)

If you don't have the original installation CD, you probably have a hidden partition on your computer. I'm afraid you may have to boot that partition and reinstall Windows from that.

Check this out:

Ideaz - JohnDa's Fundas & Ideas: BOOTMGR is missing, Press Ctrl+Alt+Del to restart (http://johndasfundas.blogspot.com/2009/08/bootmgr-is-missing-press-ctrlaltdel-to.html)

If you don't have the original installation CD, you probably have a hidden partition on your computer. I'm afraid you may have to boot that partition and reinstall Windows from that.

How do I do that

When you boot the computer, look for something that indicates to push (usually) <F10> or <F12> or something similar to change the boot order. Look for words that imply that you're going to repair or reinstall the operating system. Try booting several times. Hit <F1> through <F12> to see what effect that has. One of those keys (often <F1> or <F2>) should get you into the BIOS editor. It's possible that you can boot into the hidden partition there.

Once you've found the reinstall area, follow the instructions to reinstall the operating system. Realize that in many cases, this will cause you to lose all data on the hard drive. Some of the newer systems will save all of your data in a special subdirectory so you won't lose it. You will have to go through that information and move the files you want into "My Documents" or wherever.