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 a new idea' is the wordplay.
'at' means one lot of letters go next to another.
'end' indicates one should take the final letters.
'a new' indicates an anagram.
The last letter of 'dead' is 'd'.
'idea' anagrammed gives 'aide'.
'd' after 'aide' is 'AIDED'.
(Other definitions for aided that I've seen before include "'Assisted, helped (5)'" , "given assistance" , "not under their own steam?" .)