You can find the behaviour of the leds here
Flashing blue and white is normal while booting, solid white means " Drive powered up and ready."
You can take out the hard drive
and read the contents with a linux distro (you can connect it to your computer and run a linux distro from USB) so assuming the hard drive still works you should be able to recover everything.
As for the troubleshooting. Have you tried powering it down, unplugging the power and holding down the powerbutton for 30(ish) seconds?
If that doesn't solve it you'll probably have to connect the hard drive to a linux pc and see if you can find any error logs, since you have no other way of accessing the drive.
Oh, have you tried going to http://
<<nasipaddress>>/ in your browser? Chances are slim but if you haven't done that yet give it a try.