The official firmware has extremely small space for apps, and it has been my and a few others observation that you must underfill the appspace by 50 or 60mb for it's own housekeeping or the tab will chronically drag or lockup or whatever. It was designed to save space for media not today's megabloat apps, so you can really only install a handful.
All such things are covered in the sticky topics at the top of general gen8 area viewforum.php?f=63
. See viewtopic.php?f=63&t=64427
topic for the simplest fix. Or did you install google play correctly, as in the mostly obsolete topic viewtopic.php?f=63&t=47197
For the Generic user I thoroughly recommend Arctools on Appslib as a Market installer.
All other Market installers are 'One Off' unless you keep track of the developers site/thread.
Arctools automatically informs you of an update just as any other app would do, thereby keeping you on track.
I use it, it works well, and online Market works fine without any of this unesessary Fix/Unfix rubbish.