win 7 install possibly missing MBR

hey. spent last night racking a new hdd then installing windows 7 to it. i did this using another drive running windows 7 itself. since i own a digital copy of the OS, i downloaded the digital installer to that other drive, formatted the new drive and pointed the installer to it.

that all went smoothly. i got win 7 up and running on the new drive and updated to the latest build. problem came up when i decided to make it my primary drive: changing its boot priority to first boot i get no OS recognized. really i get the pc trying to boot to my network card, but same difference. and with the old drive unplugged and the lan disabled, it's made explicit.

the thing is i can still boot to the new drive and its fresh win 7 install, which is what i'm using to type this, but only if i keep the old drive in as the first booted drive. with both drives in that configuration my pc boots normally up to a splash screen that asks me to choose one OS and its respective drive over the other. either selection works fine and i get no issues doing this, but eventually i'd like to reformat that older drive and use it for storage while i make this new one my primary. so i'm thinking thinking the new drives boot record must be paired to the old drive somehow and altogether missing (or who knows) on its own. how does this kinda thing happen? i don't know

anyway, i've spent the last couple hours trying to repair/replace the new drive/OS' master boot record using a burned windows 7 installation disc. i've done startup repair with no luck, and no detectable problems. i've done bootsect /nt60 SYS /mbr with no luck. i've done bootrec /FixMbr and /FixBoot with not luck. i've done these steps:

bcdedit /export C:\BCD_Backup
c:
cd boot
attrib bcd -s -h -r
ren c:\boot\bcd bcd.old
bootrec /RebuildBcd

again with no luck.

is there any thing else i can do or should i reformat and reinstall? and how do i prevent the same thing from happening again? i'll appreciate any advice