2001 Toyota echo

There are countless things that it could be. Stop guessing and get a proper diagnosis. Much cheaper than a fuel pump that probably isn't as good as the factory one it replaced. The problem may be nothing more than worn-through wire insulation causing a short. If you want to diagnose it yourself a good first step is to verify fuel or spark. Try to start it then pull a spark plug to see if it's wet from fuel. Ground the spark plug and see if a spark jumps the gap when cranked. The idea is to use the easiest tests to eliminate the most possible causes. Don't guess, you're more likely to make matters worse.