Crock Pot roast beef help please.....?

One thing you have to remember with a crock pot is that it is a slow cooker so it will need some kind of fat to melt into your meat to tenderize it. If you are using something such as a sirloin roast in your crockpot, it may dry out as those cuts are traditionally pretty lean versus cheaper cuts such as rump roasts. Now I'm not suggesting that you go out and buy a roast that has a big ole hunk of fat on it, but look for a cut of meat that has plenty of marbling throughout. I have also found that drizzling some balsamic vinegar over my roasts not only gives it incredible flavor, but also act as a meat tenderizer due to it's acidic content. Best wishes!