computer won't boot up

Dear Friend,

R u using xp if yes no worries just u need to have xp cd and Repair ur windows seems booting files got corrupted

Procedure to repair

Boot ur system from XP bootable cd

Afer windows is started it give u diff option
1 Press Enter Setup Windows
2 Repair Windows
3 Press F3 to Exit.

select 1st option

Then it ask you to press F8 to Agree Agreement
Press F8
Then i check for HDD Storage

Then it shows Windows Path that is already installed give 3 option

Press ESC to Install windows
Press R to Repair Windows
F3 to Exit

Select or Press R

It will Ask u to Press L to delted old Windows File then Press L

then it will proceed to intall windows fille & Repair ur corrupted windows

Will take around 30-35mins

U r Data will be Secured

That the previous answer is incorrect, but since you said you don't have an installation disk anyway it doesn't really matter.
So try this instead-
When you get to the black screen with all the boot options, select the option to "disable reboot on error"
This will invoke chkdsk on the next reboot and hopefully you will find that you can log on to windows. If this doesn't work for you then your only hope of recovering the data is to remove the hard drive and attach it to another comuter either by USB cable or internal fitting

Can you borrow an installation CD? You don't need the serial number, just the CD. If so check out this link http://pcsupport.about.com/od/fixtheproblem/ht/repairbootini.htm

To copy your data, can you attach a USB hard drive or use a second hard drive in the ailing machine? If so you can boot from a backup CD and copy your data Acronis True Image comes to mind. Download a functioning free trial here http://www.acronis.com/homecomputing/download/trueimage/