Imac Crashed

I have an older Imac 27" when i get pass the opening screens, i hear sounds, but my Imac freezes and all can can do is Shut it down.
I have tryid installer Zwift again, but no lock.
Is it my Imac there is to old?

macOS: High Sierra
iMac (27-inch, Late 2009)
2,66 GHz Intel Core i5
12 GB 1067 MHz DDR3
ATI Radeon HD 4850 512 MB

I think it’s a couple of things. I’ve tried to use Zwift on different Macs over the years, and generally don’t have very good performance. They really aren’t “gaming systems” and the applications they excel at are definitely not games. Your video card is most likely too slow (the GPU), and it doesn’t have enough memory.
Unless you need a system for other gaming, it would be a waste to buy a new gaming computer. I’d say your best bet is to use on other Apple products. It runs well on the iOS platform (iPad), I honestly have never had an issue with that approach. I have used on the AppleTV platform for a couple of seasons, and it’s been pretty good. Minor glitches once in awhile, and the whole bluetooth connection limitation is a bit annoying (not Zwift’s fault).

I was just wandering why there only comes sound and no graphic.