Unless the seeds are duff or have rotted, they will pop up when they are ready.
It is that simple.
In nature seeds drop off in autumn and when the conditions are right they germinate.
I planted loads of things on the 13/03/08, pumpkins, squashes, marrows, tomatoes, peppers, melons and more in little pots in an unheated greenhouse and some came up within 2 weeks some have taken until this week to pop through. Just a pot of yellow pepper seeds where none have shown yet.
You can force with heat but I have found, in the past, this gives a weaker plant than you end up with from leaving them with minimal protection.
In fact, every time some one on a forum asks about something not growing as they had hoped, instead of useful advice we get several people telling us that theirs are doing wonderfully and posting photos of same.
They do not tell you what has failed for them though.
It can be like the race between the hare and the tortoise with gardening.
Poll