Nissan Micra my car will drive in every other gear but first

i was driving home the other night and my car started having problems when gearing down at lights i managed to make it home where my car died. I thought it was the battery but it wasn't then thought i'd perhaps run the petrol too low and picked up debris from my tank so i put petrol in and the car was running fine again i managed to go for quite a drive and even idled in first while waiting in traffic however now it has suddenly decided that it doesn't want to drive in first but it will in 2nd, 3rd,4th and reverse i have been told to scrap it but this seems extreme when it was working fine 2 hours earlier and it is ok in every gear but first could it be transmission fluid ?