OK, so what has happened:

When you did some tweaks you modified some "protected" applications or files on the device, so that their checksum changed. Normally I think N9QuickTweak correctly recalculates the checksums so that device works normally (this is done via refhash.pl script)

When the device boots and the cecksums are incorrect it goes to "Malf mode" where it refuses to boot and shows this screen.

Additionally, you let the device run dry of battery which further complicates things as now there is not enough charge to boot it up.

The solution to both problems is to use flasher, fist to charge the device enough for booting, and then boot it to rescue mode to remove the Malf.