delay in opening application

I am having a problem with a delay of 30 - 60 seconds following a mouse click to the opening of an application, email or internet.  It also happens when I click from site to site while on the internet.  It is happening on and off line.  This makes for very slow and frustrating computing.

My computer is a Dell 8400 with Windows XP Home 2002, service pack 3.  For firewall and antivirus/antispyware, I'm using ZoneAlarm 8.0.  I've tried shutting down ZoneAlarm, which didn't make a difference.  The windows firewall is disabled.  I checked the connection with my internet provider and ran a speed test.  I've run CCleaner, SuperAntiSpyware, Malwarebytes, Spybot & Ad-Aware.  I've used disk cleanup and defragmenter.  All file sharing software has been removed.

I would appreciate any help with this problem.

Thank you.