Windows 7 - New MB Processor, old HD, boot reversed drive letters and won't boot

MB died.  Replaced it and CPU.  Used old HD.  All workd well, but booting reverses two partitions on single HD and C is now D, D now C.  Doesn't boot.  How can I swap designations of partitions without reimaging, reformatting, restoring?

hit the start button and in the run window type diskmgmt.msc this will launch the disk manager
you will see your drive(s)  C D and anyone media storage device you have connected to the machine.

You can right click on the dive letter and change it from here.
Warning - I have never done this on a single HD I have done it on multiple drives where I wanted the Drive letter to be different for network mapping.

Don

sorry I just figured out what you are saying it wont boot.  At this point you are limited to a few options,

1. Buy a new HD and install your OS making it the master drive, let your old HD be the Slave and save all your data and when you are ready format the old one.

2. Get a Bootable CD or external device that will allow you to look for the boot.ini file.  perhaps make changes so that it points to teh partition with the OS.

I would reccomend trying to save your data by just getting a new HD.  the benift will be the extra storage in the future. 

Don