I just recently posted this on Apple Discussions, but I figured maybe someone would know the answer to this on the teamsugar site. Any advice would be appreciated!

Here is the post:

We have a Power G5 tower at my job and we haven't used it in awhile (my guess it's been months since we used it). Well, we needed to use it again and it was working fine for while. Then, one day we turned it on and it started up. However, it got to the gray apple screen, and the loader icon keeps spinning but it never made it to the log in screen.

After several tries (during the course of a couple of weeks), it eventually made it to the log in screen and starting loading the operating system. But it didn't get to the user screen (where the names are to click and log in). After awhile, the screen just goes completely blue and you can still see the cursor.

Also, I noticed that the fan in the tower is very loud during all of this.