This tablet (and some other similar cheap models) has wireless connectivity issues, particularly if wireless security is used. This seems to be mainly because the little wireless card (a "printed circuit board") inside, which includes the antenna ("aerial"), is positioned behind the screen and this blocks the signal. Soldering on a connection to another antenna has been suggested but what I have done as a temporary measure is to make the card "external". To do this I opened the unit (four tiny screws under rubber bungs on the back then carefully prize up the screen bezel from the base) and cut a slot in the side of the base opposite where the wires to the card leave the "motherboard". The wires are taken out through this, placing the wireless card outside the unit. It is protected electronically to some extent by a piece of clear tape but be aware that is does get quite warm or, indeed hot - possibly contributing to the wireless problems when mounted internally.
Though sometime getting a connection seems to need turning the wireless off and back on, once connected it has stayed connected. It would not do so before! Note however that the wireless does seem to need the battery to be fairly well charged to connect.
The above is posted in the hope that it will be helpful but no liability can be accepted if anything goes wrong.