Hello,
i have a very strange internet problem,after about an hour my wifi shows that it is connected but my sites other than google,youtube,facebook,gmail stop working,these sites work without any problem for hours but no other site works.,till i restart my PC.

please suggest an apt solution

What browser are you using? What operating system + version? Do you have personal firewall software running on the system?

i use windows 7 64 bit,and i have a free avast installed in my pc,but the problem starts only after an hour or so

Ive heard well i have this problem:
1: when i first connected to the internet with AVAST 2015 or 2014 whatsoever when my dads playing his Xbox 360

this is where the problem starts every half hour or so.
im playing on my pc with Avast installed every 30 minutes everyones internet in my house gets disconnected.

when i uninstall avast the problems gone

When i have bitdefender malwarebytes no problem

you are right ,i just tested it.but which antivirus should i install which would not cause this prob.even avg is causing the same prob.

Just to let you know that AVG did the Same too on mine last night

Malwarebytes did not cause problems
Bitdefender did not cause problems either

Just have a try and see if Bitdefender and Malwarebytes causes any problems

I have been having a similar problem but in my case it was a wifi router at fault. Reboot the router and all would be OK for another hour or two. I then took the router out of service and the problem disappeared.

Im gonna issue this connectivity issue to Avast