Is the bed warm enough? I get good results setting it to 60 degrees for PLA, although it seems to stick even better at 70 degrees. Don't just trust the display to tell you how warm it is. Feel the edges of the bed with your fingers. It should feel hot. If it doesn't feel hot, look under the bed and make sure the heating element hasn't become detached.
If you're printing something that has a small contact area with the bed, you may need to use a brim or raft for better adhesion.
Make sure the bed is clean. The oil from fingerprints can interfere with adhesion. I suggest cleaning it with a bit of isopropyl alcohol and a clean cloth.