A " BOOTMGR is compressed " message is usually caused by a combination of the below reasons.
1. There is no hidden 100 MB "System Reserved" partition in the machine. If it exists, Windows will always use it as the "Active" partition and store critical boot file in it. Usually this small partition is only created if you do a clean install of Win 7 - re-partitioning the disk. If the disk is already partitioned in an earlier version of Windows, installer will simply installs the "Bootmgr" to "C:".
2. You compressed "C:" which in turn compressed all files including "Bootmgr". The bootstrap code which is used to start Windows don't have the capability of decompressing files. As a result the bootstrap code will present you the error message.
Please try the below steps.
Connect the HDD as a slave drive ( USB enclosure/direct connection ) .
Identify the drive letter of slave drive's Windows partition. For our example , "E:".
Open a command prompt and type the below commands one by one.
attrib -s -h e:\bootmgr
compact /u e:\bootmgr
If the above steps shows any error messages, post the exact messages or screenshots with next reply. Also a screenshot of "Disk management" window will be helpful.