problems occurs after installing avast

[joe9804]

Recently I have installed Avast antivirus on my PC. But after someday there were many problems occurred on my pc. Like, the startup time of my computer increased, my PC runs slowly, I can't find many folders in the c drives. Then I contact Netgear Router Support USA and they told me to uninstall the avast. But I have just bought it so I don't want to uninstall it. If there are any other solutions then please provide it.