Check the taskbar and hover your mouse over the screen to see what the error message is saying. If there is a red X or a greyed out icon, then you need to make sure you are connected to the right network. If there is a yellow triangle with an exclamation point, it means you are connected to wifi but there is a network problem.
If you are not connected. Try restarting the laptop, double check you have the right password for the wifi you are joining.
Remember, you might be connected to wifi with no error messages but are you connected to the right one? Sometimes you might be connected to a BT Open Zone or guest wifi by mistake which disconnects you from the office network.
If there is a yellow triangle but with a connection. Try restarting the machine, if the problem persists, do the following:
Unplug the Ethernet cable (see image above) from the computer
Check the network connection icon to see if it has gone from a yellow triangle to a red X.
If it has gone to a red X, plug the cable back in, if it is still yellow, there is a problem with the network card.
If the network connection is a red X. Check the Ethernet cable is plugged into the right wall socket or switch. Sometimes the cables get damaged so try to replace it with a different one.