Nonfunctional Ubuntu boot sector


Hello, hope I get some help here. This is problem history: 1stly I only had installed Windows 7 on main partition, later I decided to install Ubuntu on another partition of the same drive, booted from pendrive and installed Ubuntu. But after install I was booting into Ubuntu boot menu which I didnot want so after some trying I successfully installed back Win7 MBR. I used EBCD to add grub2 to bootmgr and now I get Win7 boot menu with both choices, as I wanted. But unfortunatelly, the Ubuntu choice doesnot work. I get this screen:
Starting cmain() ...    (hd0,2)    [Multiboot-kludge, loadaddr=0x100000, text-annd-data=0x634e, bss=0x0, entry=0x10092c] error: unknown filesystem. grub rescue> _
I'm not sure what's wrong. If I inspect filesystem on (hd0,2) under Windows, there's still ext4fs with valid Ubuntu instllation. So maybe while I was trying to restore main drive MBR it's possible that I somehow destroyed the Ubuntu bootsector on (hd0,3) - how to reinstall it? ...or maybe The NeoSmart loader is improperly configured, I need some clue, how to fix. I remember that I was able to boot into (hd0,3) by EasyBCD entry in bootsect before I started restoring Win7 MBR on hdd...