Imac has a blicking question folder

Hi Guys

I have an imac which i have been using for designing simple artworks

some months before it had a disk verification problem and after a few here and theres i managed to fix it, THANKS to the guys here that helped

but now i have a new problem, my wireless keyboard got messed us and when i contacted the local dealer, he told me they not repairable and i just had to buy another, which i did

got back to office, fixed it to the computer and for some reason it became very slow. it takes long to take commands, so i decided to restart it and what happened is that it brought a flickering box with a question mark i have tried restarting it with all the provided information i can get but nothing can get it to start not even to the boot folder

Some one help, thanks