Heat bed doesn't get past 80

I'm completely new to this, but I went through the getting started guide and video step by step. You say in your guide to set the bed temp to 100 for the first layer and 90 for other layers for ABS. My problem is the bed never goes past 80 degrees. I tried printing with the bed temp at 70 (as shown in the pic of your user guide) but it doesn't stick to the bed and just creates a large glob of plastic. Please help.