Optiplex 7040 has no Sound

Dear All,

I have bought some Desktops. Everything is good. Audio drivers are installed. Show working. When I connect speakers and headphone in front panel & back panel nothing happens. It has no sound. I am restarted de Desktop and the sound begin to work. Some hours late, i have the same problems.

I tried to delete the driver and download the new one from DELL page, I installed it but the desktop began to reboot (blue screen)

Could you please tell me how can I fix this problem.

Regards.