Hi,
It seems as though you may have a faulty Broadcom WLAN module or that one of the antennas has come loose.
Here is a link to the service manual for an Acer Aspire 5745 series laptop. While I realize that it is not your particular model it should be close enough to be relevant. It is different from your model in that it lists Atheros and Huawei as being the type of WLAN module available rather than Broadcom (see p.171 for listing and part number).
It shows how to access the WLAN module to remove it. Scroll to p.60 to view the pre-requisites and then the procedure to remove the WLAN module.
If you find that the antennas are connected properly it may be that the part number for the WLAN module in your laptop is "stickered' on the module. If you search online using just the part number only you may find suppliers of the part. If the price is right you may wish to consider whether replacing it is an option. Alterantively it may be that the Atheros and Huawei modules most probably would also work.
https://www.manualslib.com/manual/1197/Acer-Aspire-5745.html#manual
Hopefully this is of some help.