My car won't start when i put the key in and turn it. No sound no lights no nothing. Could it be the starter?

If you have no dash lights or interior lights that means that either your battery is dead or there's a break in the electrical circuit required to power your car.

The test you need to do (or have someone else do) is to check the battery voltage. If it is strong, i.e. above 12.5 volts or even just 12 volts then the battery has enough charge to start the car, the problem is the battery connections or a bad connection in the power distribution. Simply cleaning the battery terminals and posts may fix this problem, otherwise someone needs to work their way through the electrical system to find what's gotten loose.

If the battery is discharged, i.e. the voltage is low, then what it means is that something in the car is using energy even when it is sitting. This is called a parasitic battery drain, and they can be a pain. Now, in a modern car there's always something using a bit of power (clocks, alarms) but these things are very miserly. For the battery to drain in 2 days there's 2 categories of problem:

1. Something is using power when it shouldn't, for instance a light not turning off. I left my map light on one time and it drained my battery overnight, I've heard of trunk, glove and interior lights staying because of broken switches. It may be worth taking 2 minutes to test these. Cars these days often turn their headlights off themselves, but it's still worth checking you didn't leave your lights on, it's easy to do
2. A short is draining the power from your battery. Malfunctioning radios, frayed and loose wires can draw power even when completely switched off. Testing for this involves putting a multimeter in-line with your battery and then removing fuses one by one to determine where the power leak is, sounds complicated but is actually easy to do. One thing to remember is that many modern cars pressurize the fuel system when the drivers side door is opened, you need to close the drivers side and leave it for 20 minutes before you start testing