no input signal

I have had Ntrack for a while now and have used it quite a lot with not too many problems.
But today when i turned it on for some reason it is not rcognising my 'Line in’on the recording VU meter.
I know that the soundcard is OK as my amp will come thru the computer speakers when plugged into the Line In imput.
I used it yesterday and it was fine but now suddenly i have this problem.No one touched the computer in the meantime.
I use a realtek(motherboard) soundcard and have the record and play settings on MME in the N track settings.
All the souncard settings are line activated for both.
Any ideas? (i had this same problem quite a while ago and i think i ended up reinstalling to fix it)
N track
Version 5 .1.1 number 2313