Hi,
Start hjt (right click hjt icon and select 'run as administrator'), do a system scan only, check (if found):
R0 - HKLM\Software\Microsoft\Internet Explorer\Search,SearchAssistant =
R0 - HKLM\Software\Microsoft\Internet Explorer\Search,CustomizeSearch =
R3 - URLSearchHook: (no name) - *{CFBFAE00-17A6-11D0-99CB-00C04FD64497} - (no file)
O4 - HKUS\S-1-5-21-3158653136-1639320181-1930296340-501\..\Run: [lphcg6fj0e9c5] C:\Windows\system32\lphcg6fj0e9c5.exe (User 'Guest')
Close browsers and "fix checked". Reboot.
Delete C:\Windows\system32\lphcg6fj0e9c5.exe file if found.
Post a fresh hjt log. How's the system running?