[ubuntu] Unable to boot into Ubuntu (Dual-boot Win 7 and Ubuntu)

I downloaded and installed the Ubuntu 12.04 LTS 64 bit just now. I followed the LinuxBSDOS dual-boot guide to install Ubuntu on my computer as previous attempt to install Ubuntu normally was unsuccessful (GRUB mess up the Windows MBR, none were able to boot).

So everything went pretty smoothly until the boot. After I picked the Ubuntu at the Windows boot menu, there are no Ubuntu boot screen, instead, I was greeted with an GRUB "error".

Here's the error I've encountered just now



Note: The "possible command" only shows up after I pressed the TAB button. entering the command /grub boot gives me the Error 8 message.

FYI, here's my partition scheme


250 GB NTFS Windows
500 MB boot (primary) (bootloader installed here)
40 GB / (logical)
200GB /home (logical)
4 GB swap (logical)


and the following is my system information


------------------Overview------------------

Processor : Intel(R) Pentium(R) CPU G860 @ 3.00GHz
Memory : 4096MB(Speed 1333)
Mother Board : AsRock H61M/U3S3
Video Adapter : ATI Radeon HD 5670
Disk Drive : WDC WD5000AADS-00S9B0 ATA Device(465GB, IDE)
DVD/CD-ROM Drive : TSSTcorp CDDVDW SH-222BB ATA Device


Help are much appreciated! :KS