Memory delays/ cannot activate firewall/downloads blocked

Hi Please Help…. My PC may have virus/malware problems. There is memory delay with all internet usage. I cannot activate the comodo firewall that was downloaded. message advises to re-install but it will not remove/delete from my programms in order to re-download. My Pc will also not allow certain downloads such as firewals/antivirus. I have :- Dell desktop XP pro SP1. Pentium 4 1.70Ghz 512mb ram Thankyou Andy.T

For malware removal advise… go here and follow these directions: http://forums.whatthetech.com/index.php?showtopic=106388