2000 mazda 626 LX 2.1 that just died
 

So on my way to the store my 2000 mazda 626 died out of nowhere it kinda had a rough idle but ran fine once moving when it died on me I tried starting it again and all it did was clanck and die again it hasn't started up again since I'm looking at the timing belt now but it looks good it moves on the wheel fairly easy don't know if that's good or not I also ran a code reader on it and I got code P0420 please some help would be great

P0420 is related to the catalytic convertor &/or O2 sensors.

When you turn the key what actually happens? Does it wind over? Slowly? Fast? Noisy? Quiet?

How's the oil level? How's the coolant?

What do all the spark plugs look like?

Are the camshafts still timed up to the crank?

Does it have fuel pressure?

Does it have spark?

Compression test?

What it does
 

So when I try and start it it wants to buy won't right after it died I started it up again and the was a scraping/grinding I just did a flush and oil change on it within the last month so both are fine spark plugs look good a little black but not oily my dad thinks it might be something to do with timing wether it's that or not it's getting replaced not sure how to check the fuel or compression but I'll figure it out I'm determine to fix my car and I appreciate the advice any help is greatly asked for