my 240 ont start please help...

[trigger94587]

i just change the starter and the switch under the clutch. Then the car was running fine then i turn off the engine ang test my heater then when I notice it was working fine i try to start the engine and it wont start again im guessing bout the battery but all lights and accessory are working fine can any ony help me determine the problem? i read some forum and some says its the starter relay (interlock relay the blue one) iono wat to do please help me thanks!