Bootmgr is missing to restore my computer

To enter BIOS, press F2 or DEL key immediately after turning the Computer Power button ON.

You will see a new Blue Screen with several Tabs, goto the Tab called BOOT now press the _down_ arrow key to Boot Device Priority(this name might be slightly different in yours) now press Enter.

Then set:
1st Boot Device to your CD/DVD Drive Name
2nd Boot Device to your Hard Disk

Note: The names of course, won't be HardDisk or CD/DVD you will have to figure the names out yourself.

Press Esc

Then choose Exit Saving Changes in the next Tab and choose OK.

Now enter your Bootable XP CD and

you will see a Black Screen which wil say:
Press any key to enter Setup...

Now press any key. Your Windows XP Setup will start.

Here is the same thing with Pictures:

http://www.wikihow.com/Set-Bios-to-Boot-from-a-CD-ROM

But be aware, the names might not be HardDisk or CD/DVD(in your PC) you might have to figure the names out yourself.

I do not have the disk

Do you have another Computer to use? If yes, read this page:
http://my-tech-site.blogspot.com/2012/01/how-to-make-bootable-usb-for-xp.html

That didn't work

It should. Making Bootable Pendrive and using it to setup OS instead of a Bootable Disk is nothing new.

I have tried it over 20 timds

I am using a Acer Laptop in which i had accidentally deleted my BootMgr and various other system files. My DVD was dead and i had no other way to install a new OS, i used my Desktop to create a bootable USB and used it to freshly install Windows 7 and i am replying from the very same Laptop - infact from the same install. I don't know what the situation for you is but if the USB is properly working and you have a Computer which can boot through USB then you can install one through USB.

But, you could just also use another Computer to download an ISO and burn it in a blank Disc as a Bootable CD and use it to install a new os from your Bootable Disc.

How for I do that an I' have vista

Burn ISO to Blank Disc:
https://www.lifewire.com/how-to-burn-an-iso-image-file-to-a-dvd-2626156