confusing one....
i would say that the charger is dead and you can't charge it trought USB
can you test somehow your charger? or maybe lend working-one-for-sure?
if it's dead for 5 months then you need to charge it for at least 20min to power it up
i preffer to try to charge it with working charger overnight
if still nothing
take it appart (check for junk or blown stuff while you'r inside) remove the battery and meassure it it should be >3.2v<4.2v
if not the battery may be dead
if it's <3.2v it may be dead or discharged compleatly
it's common that the Li-Ion 's die when have charge under 3v for long time
maybe try to replace the battery from friend's ps vita?
then try to power it up,if it does your charger, charging port, battery or smth like that is broken
let me know after your research...