Please provide the model of your Dell and operating system when posting. Thanks.
Normally a PBR error indicates a partition problem with the hard drive. You should immediately BACK UP YOUR IMPORTANT FILES.
Next, run the Dell diagnostics or any other diagnostic utility from a bootable CD or flash drive. What you want to do is perform a thorough test of hard drive integrity. Let me know the test results.
And when you ran the Dell diagnostics......?
And you DID back up your files, right?
I'm trying to help but you need to read my entire response and tell me what you did.
I have this same problem with the PBR Image (Y showing up nearly full (in red) and slowing down my computer. Did you ever find out what it's all about and how to fix the problem?