It shows that wireless capability is turned off(hardware radio is off) and asks me to turn on the hardware wifi switch .But my laptop lenovo z580 doesnt have an external switch.

As per the description, I understand that you are unable to turn on your WI-FI on your Lenovo Z580 laptop. I will certainly help you with the same.

First ensure that wireless services is running properly. To check that, follow steps:

Press Windows Key + R, type services.msc, hit Enter.
Right click on the service named-WLAN AutoConfig.
Check if it is set to Manual, if not then set it.

If the issue persists, I suggest that you reinstall the wireless adaptor driver, and re-create the connection again.

Following are the steps to remove Network Adaptor driver:

Click on start button and go to control panel on the right column.
Change the view by (from windows explorer) to large icons or small icons.
Double Click on Device Manager.
Expand Network Adaptor, double click on the entry of the wireless network devices.
Click the tab Driver, click Uninstall.
Open programs and features from control panel.
Remove the entries related to the wireless network adaptor.

Then reinstall the driver with your driver CD of from the manufacturer website. After installing, re-create the connection.

Note: Download the Network Adaptor driver from manufacturer website if its CD is not available.

If you will still face the issue, I suggest you to ensure that all the Windows Updates are installed on your computer as the issue may be occurring due to some missing updates.

Please follow the steps to install available Windows Updates.

Press Windows + R, type control panel and then click on ok.
Change the view by (from windows explorer) to large icons or small icons.
Click the Start button, type Windows Update in the Search box, then click Windows Update in the results pane.
Click Check for Updates. After the scan is complete, click Review optional updates.
Click the check box next to the updates, then click Install updates.
If prompted, review the license agreement, then click I Accept.
Follow the onscreen instructions to download and install the updates. If prompted, reboot your computer.