Its only a short tip to say its best to check things in order when something goes wrong.
First check the physical hardware, is the network cable plugged in, do you have power, could it be something obvious? NUMLOCK key pressed by mistake?
Next check to see what was changed last, usually the last thing changed is where we will find the issue.
Next try a reboot before calling the helpdesk. This fixes many issues - its not good if its a regular thing though as it indicates a lower level failure.
The helpdesk can then check logical settings like IP addresses and passwords etc, or group policies
If its an intermittent fault then its usually an indication of a hardware fault or duplicate configuration somewhere
If the fault is hard (always remains) then its usually easier to fix.
Try swapping cables, keyboards, mice to state the obvious, try logging in as another user - is it your profile? Is it your machine? Isolate the fault and fixes are easier. What do you find normally works for you?