This problem is caused by a fault on the video board inside your Pioneer plasma TV.
The board will need to be replaced, if a replacement is available.
A local TV repair shop may be able to repair your existing board if the fault is easy to locate - in most cases, it is caused by faulty electrolytic capacitors, which dry up and stop working.
You can expect to pay around £100-150 for a repair of this nature.
Considering you can get a new 50" LED TV for around £350, you may want to consider investing in a new TV set instead - it would certainly be more reliable in the long run.
See this decent JVC model, for example:
Do reply back if you need anything else at all!
have a great weekend,Pete.