Most likely hardware issue
Try some troubleshooting steps, then contact the manufacturer if the issue is not resolved.
-Open the device manager in the control panel. Expand Network Adapters. The wireless network device usually has WLAN somewhere on it. Uninstall the wireless device by right-clicking on it and selecting "uninstall". Then restart the laptop.
-Not fixed? Again, in the device manager, right-click on the same wireless device and select properties. In the dialog box that appears, hopefully there will be an advanced tab. Here, you can try changing things such as the roaming sensitivity level, wireless mode, etc. Try changing the wireless mode from b/g/n to b/g, although this normally shouldn't affect signal strength.
Assuming that the problem is caused by faulty hardware, usually this is not too difficult to fix. In most laptops, the wireless capability is provided by a separate, small wireless module or network interface card(NIC). The NIC plugs into a slot, is held in place by a screw, and has wires connected to it which run to antannae on the top of the LCD back panel. Most wireless problems are fixed just by replacing the wireless NIC. On some models of laptop, you can very easily access the wireless NIC by unscrewing a bottom panel or door. But you'll probably want the manufacturer to replace the wireless NIC for you and TEST the wireless.