A friend brought me a Compaq CQ10 over earlier. It seems it lost power during a Softpaq BIOS update. Initially the screen was booting to the HP BIOS recovery screen, attempting to rewrite and failing around 10%. I tried a few things and nothing worked, until the owner mentioned they’d upgraded the RAM.
Sure enough, it was a different size and type to the original specification so I refitted a 1 Gb 666MHz stick I had lying around from a previous upgrade and rebooted.
This time we re-flashed, verified and rebooted. Then it kept repeating this cycle so I took off the back panel (use the orange latch visible when the battery is removed) and removed the CMOS battery. After a short pause (30 seconds or so) I put it back and rebooted. This time there was an error message about the CMOS settings (unsurprisingly) and it rebooted.
However this time we got the Compaq BIOS boot screen, so I hit the escape key to enter BIOS. Then hit F9 to load default values, accept it and hit F10 to save values and hey presto the system is back up and running.