Some days ago,I lost sound and received info says that I have no audio card
installed;the PC is only 3 monthhs old and everything worked in a nomal way
until 8 days ago.Tried to restore things to a prior date but at the end of the restore,
receive mesaage that the PC could not be restored and nothing was changed.
No alarming signs in the audio sytem-section.
Something to propose as solution?Thank you!
BTW:tried PitStop and similar:they "found" lots of errors that they "repaired" after
collecting my money,but no help for this specific problem.

Do you have a sound card installed or were you using the sound chip on the motherboard?
This is either a driver problem or the sound chip {either on the card or M/B} has failed.
Does the sound device show up in the device manager? Are the sound drivers shown under add or remove programs? If so, delete the device in device manager and uninstall the drivers.
If the device is still good, Windows should detect it as new hardware when you reboot your computer.
Good luck :)