@mrgreen Modern NICs can tell if you're using a crossover or not and configure themselves accordingly - I've used both types of cable with no issues.
But if the OP's not got NICs capable of this, they should check it, you're right.
Just to add.... there is not enough information in this post at all. WE would need a lot more info. Start with, "How do you know it broke?". What are the symptoms? How is the network setup or how did you set it up? Describe the network to the best of your knowledge. Did you change/add/edit something before the network broke?