Debian 7.X : 2TB HD installation successful but not booting

[Muhammad Yousuf Khan <sirtcp@gmail.com>]

i have a 2TB hard disk and installation went fine no errors. however i can not manage to boot it from hard disk. my partitions are like this.

1. /boot : Boot Flag ON. 

1. Swap : Boot Flag Off. 

1. /       : Boot Flag off. 

but the weird part is when i press "F10" and select harddrive to boot it amazingly boot. it seems like more of a BIOS issue but the same system is booting fine with a 250GB drive.

any idea what is going on.

Thanks,

MYK