my car won't start

[herdi]

hi...i'm new in mercedes. i have 91 w 126 300 se. everything works just fine untill yesterday that it won't start on my lunch break. it was just fine when i went to work in the morning, but it just don't want to start in the afternoon. it cranked good, i checked the the plug and there was a spark. my fuel pump also worked. i am in dead end now.i was wondering if you guys could help me what the possiblelity it might be.

best regard,

herdi