|BIOS ROM checksum error - Looks like your BIOS may have lost its settings.|
I suspect that this may be due to the fact that the motherboard battery voltage is no longer above the level where it can sustain the CMOS BIOS settings.
To see if this is the case go into your BIOS at boot up (usually the Del, F2 or Esc key) and either use the option to set fail safe defaults or optimum defaults and then F10 or save and exit and see if it boots correctly.
Also while you are in the BIOS check that it is detecting your hard disk correctly.
That is if the checksum error is a red herring than it seems your boot process goes past the detecting CD stage (having not found a CD in the drive) and fails possibly because it does not see a hard disk. Although in this case I would expect to see a further error message which you have either not reported or not seen.
One other thing I noticed that you were saying you were trying to run an update.
Was that a BIOS update? If it was then did it finish successfully? If it did, did you cycle the power?
After a successful BIOS update you should normally power off and ON your PC.
☺ When everything else fails, read the instructions.