At a dead end, a new idea helped (5)
I believe the answer is:
aided
'helped' is the definition.
('aid' can be a synonym of 'help')
'at a dead end' is the wordplay.
'at' becomes 'aide' (I can't justify this - if you can you should believe this answer much more).
'end' suggests the final letters.
The final letter of 'dead' is 'd'.
'aide'+'d'='AIDED'
'a new idea' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for aided that I've seen before include "'Assisted, helped (5)'" , "given assistance" , "not under their own steam?" .)