Seems to me it sounds like you have two versions of operating systems in 1 tower and your trying to run both at the same time once youve cut the power on. Rule 1, never install multiple OS on 1 tower unless your running some type of network, not even then its still safe.

When you do that what you just did, it causes conflict in the start up BIOS meaning sometimes or most of the time or all the time, it dosent know which OS to load up.

Another thing i am thinking here is that you have two diffrent user name and password, but Im sure you have the same on both. If I were you, Id try to just reinstall 1 of those OS. The other OS can be used on another tower.
Im hoping all that was said by me made some type of sense or at least has something to do with this ding dang post. But then again, Im always sleepy when I type at this time of morning.

From the Microsoft knowledge base:

To take ownership of a folder, follow these steps:
1. Right-click the folder that you want to take ownership of, and then click Properties.
2. Click the Security tab, and then click OK on the Security message (if one appears).
3. Click Advanced, and then click the Owner tab.
4. In the Name list, click your user name, or click Administrator if you are logged in as Administrator, or click the Administrators group. If you want to take ownership of the contents of that folder, select the Replace owner on subcontainers and objects check box.