I have bought my father BV6000 and the phone is great for his use, but it has one problem. Every time I connect to a network (WiFi or mobile network) it connects, works for 10 sec, and the it disconnects. It is very annoying, and it means he can't use any network. Is there a fix for this problem?

1) Please check if you have activated any battery saving mode

2) Go to Wifi settings ans check that "keep Wi-Fi on during sleep" is set to "always"

3) update to the latest Firmware and perform a factory reset in recovery after that.
wipe data/factory reset in recovery (this will delete your data/settings):
- Power off and then press Power and Volume up together for around 10 Seconds
- be sure that the little arrow point on recovery (select with volume up, enter with volume down)
- Then the open android with red triangle+"no command" is shown press Power and Volume up together again
- Select Wipe data/factory reset with volume keys, confirm with power
- After factory reset select reboot system now

Please report if this solved your issue or not.