PC3L usually just means low voltage - not required for your machine, but it shouldn't cause any issues. Having said that it's possible your laptop just doesn't like the RAM, Crucial's advisor tool isn't an absolute guarantee of compatibility unfortunately.
If you've already tried the sticks individually, there's not a huge amount more to try, but have you tried one new stick and one old/working stick together? I doubt it'll work but it may be worth trying just to see what happens.
It's also worth checking if there are any BIOS updates (current version looks to be F.39) and if so, updating the BIOS, then trying again. Specifically the F18 BIOS update notes say "- Fixes an issue where a system with 4GB memory unexpectedly stops responding." which may be relevant. Looks like they've released a heck of a lot of updates, too, most say something along the lines of "added support for new models" but it's possible there are compatibility updates in some revisions so it's worth a try.
Edit: didn't see your post above, apologies! Most is still relevant, though
