Long distance Wireless Access Point

[#1]

I have a Plusnet router and I need a wireless access point in my garage, 50m away.  I have run the cable out, crimped the RJ45s and tested them - all 8 lights on.  When I connect the WAP (a TP Link, but I get the same results with my Apple airport express) I get a signal for about 5 seconds, then nothing, then after a minute perhaps another 5 seconds, then a minute or so latter another 5 seconds.

Anyone any ideas?  When I link the WAP with a 1 meter cable it works fine...

Thank you

Colin

[#2]

Have you tried connecting a wired connection in place of the WAP?

[#3]

What happens if you connect a computer rather than a WAP at the far end?

Have the RJ45 plugs got distorted during crimping causing poor connections? The tester may have more resilient sockets. I have had so many problems in the past that I now only use wall sockets which are much easier to wire. They also look neater. Obviously you need patch cables as well but these are as cheap as chips.