Hi Vigtime
I recommend you to flash BIOS and update wireless driver from the link below:
Enter the Service tag and click ‘Submit’. Select the Operating system from the drop down list and then click BIOS and download the latest version. Follow the onscreen instruction to install the same. Once the system restarts and comes up to the desktop update the wireless driver. Click on Network and download the appropriate wireless driver. Restart the system after the driver installation.
Also change wireless adapter settings. Click "Start," right-click "Computer," click "Manage," then "Device Manager," expand "Network Adapters," right-click on the wireless adapter and select "Properties." Click on the "Advanced" tab and look for a power setting option such as "Transmit power," left-click on it, and change the dropdown setting under "Value" to the highest setting.
Revert for further queries.