UK Car Repair: pressurising water system, head gasket problem, laguna diesel

Question
I have a Renault Laguna diesel and i have not used the car for a few weeks and since starting the car all the heaters do not work do not blow any hot air and the water pipes are all solid unless i slacken the radiator cap on the expansion tank do not know if it is safe to drive  hope you can help

Answer
No I would say it is not safe to drive. When you say "solid" do you mean pressurised and hard to squeeze?  If so, does this happen very fast.  You may have a head gasket problem you should start off by doing a compression test.  It could though be a thermostat problem, test this next.