The on/off switch is not working on my Toshiba 28N33B and no light comes on when you push it in. Is it a straightforward repair if I buy a new switch to fit myself ? Other than switch what other parts might I need? Many thanks Franco

Yes, the power switch replacement is a very simple job - you just need to keep the wires soldered in the same position on the new switch: make a diagram before unsoldering them from the old one.
If the defect is indeed located only at the switch (check that by simply measuring the presence of the mains power on the mainboard connector when the switch is pressed) then no other part is necessary.
If there is power when the switch is pressed then the defect is in the power section and it will have to be investigated further.