I have been experiencing lockup issues with my TouchSmart IQ816 for some time now and I am having difficulty in determining the root cause.  The system is a refurbished system from newegg.com and initially came with Windows Vista.  I purchased the system in July which made me eligible for the upgrade to Windows 7 which I installed leaving off any HP software.  Just the OS and media center. 

The problem appears to have always been there and I initially thought it was related to the Seagate HD not having the updated firmware.  It was shipped with HP24 and would randomly lock up with a disk read error.  Running the BIOS tests, it would occasionally produce a BIOHD-5 error further indicating the Seagate HD problem.  Checking these forums, I found that there is a known Seagate HD issue and a firmware update was available.  I updated the firmware to HP26 and the disk read errors went away, but a new problem began to occur.  After random periods of time watching TV via windows media center, the system would freeze and I noticed the HD led would be light solid.  The system was completely unresponsive, even to a CTL-ALT-DEL.  I would have to power the system down and then restart it.  Running the BIOS diagnostics, I would occasionally get a BIOHD-1 error.  I had a spare Western Digital 500G HD so I then replaced it and rebuilt the OS again using Windows 7.  Everything installed cleanly and the system appeared to run fine.  After a week or so, it locked up again with the same symptoms.  While watching TV, the system would lock up and the HD led would be solid.  I would have to push and hold the power button to get it to power off and then restart.  As time has gone on, the frequency of the lockup has increased and now the system will lockup fairly quickly.  It will lockup now without even watching TV.  It will lockup shortly after bootup with no other app running.  I have made sure the SATA cables are all inserted fully and cannot find anything loose or broken.  I have verified that the BIOS is the current 5.10.  I have also verified that all the fans are running so I don’t think it is an overheating issue.  My fear is it may be the disk controller on the motherboard.  I have run the BIOS diagnostics right after a reboot from a lockup and it will produce a BIOHD-1 error.  I checked with HP and they weren't very helpful.  They suggested sending it in for service which is out of the question given it's out of warranty.  I'm leaning toward a motherboard (disk controller) issue, but HP won't even give me a part number to do the repairs myself.