I have a 2003 blazer extreme 2wheel drive 4.3 vortec engine I try starting the engine

This engine is equipped with a timing chain, not a timing belt. Indeed, the chain could be compromised, could have stretched, jumped time, or had another internal issue related to timing. You could have an engine compression issue as well. Some hands on testing will be needed. https://repairpal.com/repair-shops/chevrolet-repair-and-service-in-la-fontaine-indiana

Before attempting anything else - replace the distributor cap and rotor! ... This is a relatively inexpensive gamble and is based upon extensive hands-on experience with the 4.3L engine. Due to the unique design of these dist caps you probably won’t see anything wrong by simply looking at it. Make certain the dist rotor goes back on in same clock position.. IF uncomfortable with parts replacement seek assistance from qualified personnel.. Believe me - there is no ‘engine timing’ concern here - it just don’t happen on this engine - period! Good luck!