The Google Nexus 7 tablet is a pretty well built device for a $199 tablet. But it looks like not all models were built equally — many users are reporting that the isn’t firmly attached to the base of the tablet, and pressing down on one part of the screen could cause another part to lift.
Fortunately there are a few easy ways to fix the problem. First, you can just contact Google and take advantage of the 15 day return policy and hope that your next model is in better shape.
Or you could take matters into your own hands.

Xda-developers forum member jam10238 popped the back off his tablet, found a few loose screws that seemed to be propping up the screen, and tightened them. Upon closing up the tablet again, the issue appeared to be resolved… at least temporarily.
Some folks report that the issue re-appears after a while, so this may not be a permanent fix. If anything goes wrong and you scratch up the insides of your tablet while trying to open it, you might have a hard time convincing Google or the store you purchased the Nexus 7 from that your warranty is still valid.
In other words, you might be better off just returning your tablet unless you’re impatient or you would just really prefer to do things yourself.
If you fall into the later camp though, the folks at Droid-Life have posted a walkthrough with some helpful photos.
Not all Nexus 7 tablets seem to be affected by this issue. Mine arrived a few days ago, and I haven’t had any problems at all with the screen so far.
If the screws go on plastic DO NOT USE LOCTITE. Use CA or nail polish.
Do you recommend using the clear nail polish? I’ve performed the process to tighten the screws but they came loose again and the screen is lifting again.
my screen is perfect … but my usb port doesn’t work. cant charge the tablet or connect to a pc to transfer files, it will however charge while off
A small dot of Loctite or other cyanoacrylate glue on the threads of those loose screws (before tightening them) should fix the matter for good.