I have a 99' LS series. When the engine is cold i can crank it over all day and it won't start. But if I tap the key it will try to start, after tapping the key 5 or 6 times it will start. When the engine is warm it starts right up, warm days are no problem. Fuel pump primes on start up , and I get no engine light or codes

 

Start by checking the fuel pressure. Also if you haven't replaced the filter lately - do so.

 

Fuel pressure is at 52 , also replaced filter.

 

how cold

 

GM sez you should have between 60-66. My best friends 2000 had a starting problem and also had 52 psi. New pump solved it. It's "possible" that it's a different problem like a leaky regulator but my guess is go shop prices for a pump. I know it sounds like a lot of pressure but you don't have enough for the enrichment for cold starts and the day will come soon you won't have warm starts either.