I recently purchased Minecraft for the PC after playing the demo. 

I was able to freely destroy blocks normally with my tools or dirt and stone with my hands (in the demo). However, now I am trying to destroy blocks in survival mode on the full game, the blocks disappear for a split second and then appear again, then disappear completely around 10 minutes later. 

This really slows down gameplay and I haven't been able to easily mine wood to make a pickaxe. One time I managed to make one, but thee results didn't change and the blocks kept clipping back and taking forever to actually disappear. 

Is there a reason why?