Novatech NSPIRE 1537 BIOS

Dear All,
I have a problem with my Novatech NSPIRE 1537. While switching it off it doesn’t shut down. The screen goes black, but the lights stay on, the fan is humming and one can hear the hard drive working and nothing else happens until the power button is pressed on.
Strangely enough the another laptop of the same make and model bought at the same time does the same shutdown failure. It is not the Operational system fault since the linux run from a CDrom drive produces the same shutdown failure as under windows 7.
It looks like a corrupted BIOS issue. I would like to try to install a new version of the current BIOS version and would be very grateful if somebody could tell where I can download a newer version for my laptop - and possibly some in
It is NSPIRE 1537 NNB-A33 serial 135PE5220295. The current BIOS is A15W8