Please Help?

Hi,I have been having problems with my computer.Around the 14th my computer started acting up.Programs wouldn't open  or would  take 30 minutes or a hour to open or would freeze and not respond.I.E. and mozilla wouldn't open.I tried to run a norton full scan but after 21 hours it had only scanned to 50,000.On April 16th I called norton to see if this was a virus but since I couldn't get online they could not help.I did finally manage to get mozilla open.The only way it would open was to unplug from the dsl,click on mozilla,the page would come up saying working offline,hook back up to dsl then click try again.I downloaded malwarebytes and ran a scan.It did find and remove adware.minibug.The computer worked fine till 4-24.Same problems.Did the live chat with dell but I couldn't afford the $130 something dollars for them to check and see if this was a virus.Then computer started to work more normal.Today computer is slow,not as bad but does stop responding at times and programs sometimes take a long time to open.Since this has started I have run many norton scans,malwarebyte scans,advance windows care,disk defrag.Do you think this could be a virus or something else?  I am someone who knows nothing about computers.Please help.I am sorry this so long.

WINDOWS XP HOME EDITION

SERVICE PACK 3

NORTON INTERNET SECURITY 16.8.0.41