Sleep when locked

[michael.holls96]

I have recently bought an Ainol Novo 7 Fire running Android 4.0.4 and I have what appears to be a software problem (I hope). When I lock it either using the lock button or waiting for the screen to timeout it sleeps and disconnects from Wifi which can get annoying as it doesn't alert me to e-mails when I receive them. I have gone into Settings>Wifi>advanced and set "Keep wifi on during sleep" to Always but this has made no difference. Interestingly, if the device is plugged in then the wifi will remain connected.

This sleep problem also causes lag when unlocking. There is a wait of about 3 seconds between pressing the unlock button and the screen lighting up.

Any help would be appreciated.

Thanks.
Michael H.