I've brewed a kit that was DME and a year old - but still soft. Being rock hard I think indicates that a little humidity got in.
Anyhow the thing to do is taste it for flavor. It might taste stale (like stale crackers or bread). If it is, then that flavor will carry into whatever beer you make. Otherwise, adding them into a AG and making a Partial Mash out of it is a good idea, just make sure you include enough Hops to cover what I'm guessing is about 6LB of malt - or about +.045 to your gravity. If it wasn't a brick, I'd suggest using DME for starters like LBussy said. But given it being a brick, I think tasting and making makes sense.
Oh and some people associate the LME with the 'extract twang'. Some anticdotal evidence (ie one guy testing a few times) suggests that come from old LME.