Why is it that gear number 5 on my renault megane 2000 model is failing to get in?

SOURCE: radio code for renault megane 2000 1.6

Here is a link for your problem, good solution..
http://www.fixya.com/support/t564842-renault_megane_1998_lost_radio_code

SOURCE: renault megane stuck in 4th gear

it might be the power feed is down to the transmission. If all the shift solenoids are off, the trans will stay in 4th. Check the trans fuse.

SOURCE: Renault megane tdc location?

http://www.forum-auto.com/les-clubs/section21/sujet214136-280.htm

SOURCE: owners manual for renault megan required

here is an online free workshop manual....GOOD LUCK!   http://www.scribd.com/doc/7814761/Renault-Workshop-Repair-Manual-Manual-Gearboxes

SOURCE: Rain Sensor wipers Renault Megane

Either the replacement sensor the windscreen technician should have fitted isnt connected properly to the glass or it has developed an intermittant fault - quite common with Renaults especially megane scenics and grand scenics....