This problem is recent and intermittent. The only software that I have installed recently are standard apple updates. On startup, a solid blue screen appears before the user login screen. That's as far as it gets. I have to hold the start button to shut down and restart again. I have run Disk Utilities and Disk Warrier (from the disk) but the problem has continued (every few startups).
Hold the shift key down when starting up. The login window should appear. This will get you logged in Safe Mode. Back up whatever files you need. You can try throwing in the install disk to run the hardware test. Also check and see what you have starting up. I experienced this same issue as you. Others have logged that it was a precursor to the hard drive failing. Mine seems to be fine so far however I did find a file in start up pertaining to a printer I had hooked up. Afterwards when I did ran repair permissions a prompt appeared telling me the security settings for this file were incorrect. I had the option of fix, ignore or decide later. I chose the latter and the second prompt that followed said I might have issues starting up if the file was not fixed. I removed it from start up and my PB seems to be fine. I cannot say for certain that this was the source of the issue for me. Back up you data and be prepared for the possibility you may need to send your PB in for service.
