Customer details vanish after klicking " submit order"

[CyberDaph]

I've got an old Magento store on http://www.goingsolar.nl. It's an 1.7.0

Everything workt well until now. When a customer wants to place an order, after filling in all the details and klick on "submit order" you get the same page again, but all the details vanished. The order is not being prossesed either.

Can someone help?

Thanks!

[Brent W Peterson]

Have you checked that you server is not out of space? How are you storing your sessons? Have you added anything new, like custom modules?