puneet

Check the starter relay, check the spark plugs, check the fuel filter and air filter. Either of one will find you the solution. Good luck.

Never heard of brake pressure sensor. If you mean brake sensor, then its inside the brake pad and it wears off while brake pad is getting wear off.

Im not sure 100% but if you cant find it next to fuel tank on left or right side near the fuel rail and not even under the rear passenger seat, then its more than likely that its inside the fuel tank.

i have a SLk 2003 and every now and then i try to start the ignition switch a red&green light flash continuously on my rear view mirror and the engine wont start. at times if i leave it for few hours and try again it starts and at other times it takes overnight. what could have gone wrong please advice