How can I stop security light flashing so I can start car.

If your security light is flashing -- and it's a factory equipped security system -- then you likely have keys that are not programmed to work with the immobilizer system of the vehicle. What keys are being used? Do all keys used do this? Have keys ever been replaced? Are there any aftermarket security or electronic components added to your vehicle? So many questions; a hands on diagnostic test will certainly be needed. Here's a way to find some shops near you: www.repairpal.com/repair-shops