I had to drill out my ignition on my 99 Chevy Tahoe because I recently lost both sets of keys and now it just turns over and doesn't start I just hear a ticking noise... What can be the problem..

 

if it didn't turn over and made a ticking noise...its could be a dead battery. you can hear a ticking noise over a cranking engine? post a video

 

It's in anti theft mode now. Drilling out key damaged the assembly just like someone was trying to steal it.
You need a new key assembly and housing and a reprograming for the new parts.
Paying a locksmith would have been cheaper and easier.