And you missed the fun of getting 8 tiny wires into the plug in the right order before crimping them Mr Lovelength.
Get one of those cheap cable testers from the bay of e. At least you have a chance of diagnosing a cable fault then.
no i thought i would be a smart arse and brought preassembled cables then ran tham to the main wiring cupboard and cut the other end and wired them into an outlet..........not tried the crimping bit yet but i got the tool....looks the part. About 20 cables ran throughout the house carefully routed to avoid power etc only to be told by our leader they are shite

Where they are twisted pair cables, mains noise should have no affect. More important is to avoid tight bends, this should be a minimum of 25mm, which is why the corners for network trunking are curved.
I've never had any problems with pre-made cables from out local network equipment wholesaler, but when running cables I always make then bespoke.
Crimping Cat 5 plugs is a bit like the Omega Engine B-bolt, but with a bit of practice 95 out of 100 will be right first time. Most common mistake is one of the wires being slightly short in the connector so you have an open circuit.

A tester makes it easy to check both ends are correct.