I bought two HP Pavilion 23xi monitors about eighteen months ago from PC World. One of them developed a problem where the left half of the panel went blue with horizontal lines. This monitor was replaced by PC World. Three months later the second monitor, attached to a different computer, on a different port, and with a different OS, developed the same problem. This monitor was replaced by HP under the call reference 9520323016. Fast forward to February of this year, and one of the replacements (serial number 3CM3230B1R) starts displaying the same problem. I contacted HP Customer Service but was told it was out of warranty. Then, just today, the other replacement monitor (serial number 3CM310013V) starts suffering from THE EXACT SAME PROBLEM. I contacted HP Customer Service yet again but was told that this monitor was also out of warranty. I explained that I had had four 23xi's develop the same problem in only eighteen months but was told that there was no known problem with the model and that I would have to pay to have either one replaced.
If it was a one off I would totally understand that I would have to pay to have it fixed or replaced out of warranty. But this problem has happened four times, in eighteen months, to four IDENTICAL monitors. Not only that, but it appears the fault is well documented on the Internet. I found five threads on the HP Customer Service forums alone filled with no fewer than EIGHTEEN people reporting the same problem.
http://h30499.www3.hp.com/t5/Monitors/Half-of-monitor-is-discoloured/td-p/6202151
http://h30434.www3.hp.com/t5/Desktop-Audio-Video-Monitors/Hp-23xi-problem/td-p/3359367
If you care about your customers HP, you'll use some discretion and fix or replace my monitors.