Why are my squash plants falling over dead??!!?

My straight neck squash plants have grown big and healthy this year but %50 of them are breaking off at the base of the plant and dying/welting.... They are just fixing to flower and I am wondering if this is normal or what is going on??? I have them planted in mound (2-3 per mound) and really do not want to lose any more. PLEASE HELP!!!! Thanks in advance for any helpful info.