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#21
You don't need to make it your default driver. If you install Windows 7 on it anew, you will get a boot screen allowing you to select whcih OS to boot from (they wil both be called "Windows 7"), which will also mean whcih drive to boot from.
Better yet, you can disconnect the HDD which you have the OS now (and is causing the issue) and install in the other driver, then boot only with that other driver. You will avoid messing up your boot sector. If everything turns out the same you can wipe the smaller one and we are back to square one. If it solves it, then the larger HDD is the problem.
Beware, my suggestion means you would wipe your secondary HDD clean, so you should only do it if you are not using the data in it. Another option is to create a partition in it and install it there, then you preserve the data. In any case it is advisable to backup everything first.