Credit button not actuating switch or broken wire? Do you have access to the inside of the game?

So you coin in, get your credits, then you push start and the (all? or just one?)credits go away, but no game starts?
My reflex answer is that it sounds like a cabinet tilt switch is stuck.

However more information as to what is happening would help.
For example:
Does it try to put a ball in the shooter lane?
Any solenoids going off?
Any sounds?
Game over or tilt lights blinking?

That's a money maker!

So coins are not putting credits on.

Sounds like the coins are not hitting the credit switch or some problem with the credit switch.

Try this thread, maybe you'll get an inspiration on where to look if you ask mof.

https://pinside.com/pinball/forum/topic/high-speed-restoration

Did you check the slam tilt switches?

HS should have a switch test mode go into that and see if anything is screwy. Probably will need the balls out or the ball trough switches will go off.

Nope, should be in plain view.

Number 20 on the right page.
http://www.planetarypinball.com/reference/partsmanuals/WMS_Parts_Blue_16-9064-B/index.html#/646/

or maybe # 18 on this left page but either one is in about the same spot.
http://www.planetarypinball.com/reference/partsmanuals/WMS_Parts_Blue_16-9064-B/index.html#/628/

but in general you are looking for a switch that has a small round weight on it,
like the bottom right of the left page here.
http://www.planetarypinball.com/reference/partsmanuals/WMS_Parts_Blue_16-9064-B/index.html#/94/

Could be on the back of the coin door, in the cabinet floor or side, under the playfield, maybe even one in the backbox, check for all of them I'm not sure how many tilts or where exactly they are on HS.

Not sure but a closed slam tilt puts the pin into "game over" mode.

Check out page 4 of the manual. See if your pin is in Attract mode or Game over mode or what. Knowing what state the game is in helps with trouble shooting.

For example here is what is says under game over mode:

"GAME OVER MODE. The GAME OVER indicator lights. The SPEEDER 1 and SPEEDER 2 displays show GAME OVER. Then, the high scores flash on the appropriate player score displays. The game proceeds to the ATTRACT MODE."

So if the switch is stuck closed the game might stay in game over mode and never get back to attract mode.

This is all just guess work on my end. How did the switch levels test pg (25) go?
Link to manual if you don't have: http://www.planetarypinball.com/reference/gamemanuals/High_Speed/index.html#/4/

So, you put in a quarter and the game acknowledges it, but doesn't post a credit... hmmmm... how about if you put in a whole bunch of quarters? Maybe the pricing is screwed up.....like $5 for one play. Can you get into audits and set the game for free play?