CPU usage 100%

[nyamoga12]

Hey guys,
I have windows XP SP3 on a Dell Inspiron 1501. Recently AVG kind of misbehaved, ie it refused to update and was giving me alerts, so i uninstalled it and put Symantec. This worked for me but of recent, it won't update, and my CPU usage is always 100%. The computer has become sooooo slow.
I ran Malwarebyte's Anti-Malware, it scanned and got some nasties, but still the computer isn't fine, plus it's starting to take really long to shutdown, yesterday i spent like 30 minutes waiting until i gave up!

Please help :(

[paulas24]

maybe you might try repairing the windows using recovery console then update your antivirus to clean your computer again

[gerbil]

" Recently AVG kind of misbehaved, ie it refused to update and was giving me alerts".. what kind of alerts? About viruses, or AVG problems?
Did you scan your computer with an online AV before installing Symantec?
Perhaps it is still infected. Do you have the original MBAM scan log? Post it..

[Master Rattley]

Systems restore to when it was working well?, than install Microsoft security essentials, best free protection out there.