Nokia N73 - suddenly turned itself off, won't turn back on!?

[Littlebitoflight]

My phone has never had a problem before, it showed no signs of poor battery life, or any stalling or working slowly lately.
I usually leave my phone on 24/7, unless it crashes, then I restart it.
Last night as usual, left my phone on with the alarm set as I usually do.
Got woken up by my house mates alarm clock so went to check the time, phone was off. I figured ok battery must have died. Despite still being half full battery last night, which normally lasts a good day or so.

So I plugged my phone in to charge, and it eventually beeped to say it was connected, but there was no charging icon, and a fully black screen. I unplugged it, took out battery and sim for a while, put it all back together again plugged it in... Beep took a lot longer.

Searched forums and needed to get the number out of back of phone, so had to unplug (the still not visibly charging) phone to get that. Plugged it in after that, no beep.

Any one else had this problem, and why would my phone just suddenly have cut out? Also what do I do next? Thanks

Also my phone is about 16 months old.