Oh what fun, yep you can boot with (1) stick of each. The reason I need the JEDEC info is to see if there's any overlapping CAS and I forgot also post the {Nominal Voltage} for each stick.
IF I can see an overlapping Frequency, CAS Timings, and Voltage the next step is to attempt manually setting the BIOS. My assumption is the 'SPD' information seen by the BIOS is reading two different CAS timings and causing the problems.
Further, IF the PC won't boot with the new 4GB it too might be bad. So in either case you're not wasting your time. Just be careful removing/installing the RAM and be sure to touch the PSU to de-static yourself...