Removing those two screws requires an open case to get at the screw-head. Put plainly, you're not going to get those screws out while the case is still on your system.
You don't want those out right now anyways, you'll need to remove those two only if you decide to install/upgrade a PCI peripheral card. Which is not applicable in your case.
You should try a different approach. There must be other screws, or a slide lever, or something else you can pry at to get in there (skip to 2:35 of video to see the guts). I can see that the case in the video does slide towards the back and then lift away. It may be just sticking, so use more pressure? Use a slot-head screwdriver wedged to pry the case towards the back of the system.
1Those screws look like they're holding in the PCI slot covers. You do not need to remove those to open the case. – kobaltz – 2012-10-05T22:33:45.367
If the PC is as the one here then all you have to do is to pull the side+top - it should be L shaped sheet - off by unsnapping.
– Darius – 2012-10-05T22:37:08.460@kobaltz AH, okay. That's why it's covered... – test – 2012-10-05T22:38:54.533