Avast Blocks Windows Explorer from opening

Hi Guys. I really hope you can help me. When I boot up the computer, Avast tells me it has blocked Winlogon.exe, then blocks explorer.exe and then if I try to open Windows Explorer, it says ‘it cannot find the specified path, you may not have access rights to this program’. It mentions Win32 patched-RP [Trj]. I have also noticed I cannot access any sites on the internet that might have any software that might help me solve this. I am running XP Pro with service pack 3 and have the Avast Internet Security version 5.0.677. I keep running boot scans etc but nothing has helped. Malwarebytes hasn’t solved the problem either. I really could do with your help. Thanks in advance. Cacofonix

try mbam http://www.malwarebytes.org/

and w8 for essexyboy you ll need to use OTL and combofix