grub error 15 file not found

[just68]

have just installed ubuntu 9 on a single hard drive with XP already on it. The install went great with zero problems and ran fine for a couple weeks. Have been learning a lot {not knowing squat} such as nvidia driver for video,works great,,wireless usb adapter driver, works great. I downloaded some packages and afterwards the computer screen went to blank, i ended up just manually shutting off which i now regret. I keep getting the error 15 file not found. I have tried everything I've read about but keep getting stuck. Are the commands the same for the errors on all linux platforms or do i have to use exclusively Ubuntu? Trust me, I feel like an idiot having to ask for help, after succesfully reading and repairing thus far. It has occured to me i could just do a re install like I've read, but then i thnk this problem will arise again and I don't want to keep reloading. Here's what i got so far. I put in the live cd and went to the terminal.
ubuntu@ubuntu:~$ sudo fdisk -l

Disk /dev/sda: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x69205244

Device Boot Start End Blocks Id System
/dev/sda1 * 1 38912 312560608+ 7 HPFS/NTFS
ubuntu@ubuntu:~$ cat /boot/grub/menu.lst
cat: /boot/grub/menu.lst: No such file or directory

I really love this OS so far but i find my ignorance is discouraging. Thanks in advance for any help. Oh yeah, Devils Casper, thanks, you have helped me out a lot already from reading your advice. I see your name everywhere.

[Jonathan183]

I suggest you do a re-install and only install software using the repositories and either synaptic package manager or apt-get.

From the output for fdisk you gave Windows is using the whole hard drive ... did you re-install Windows and use the whole hard drive?

[just68]

No, I had windows installed on the whole hd first, when I installed ubuntu it gave me an option of how much space to use so i think i sd 40 gig,,it all loaded and was running fine on both OS for about 2 weeks or so. I did only do installs from synaptic as I haven't learned any other way yet. Havent' got that far. thanks

[Lostfarmer]

It would seem that for some reason your MPT (Master Partition Table) was rewritten , you will need to try to fix it. Can try 'testdisk', there are versions for DOS/XP/Linux, some live linux cd have the program. Read the How-To
TestDisk - CGSecurity