Windows xp start up delays at welcome screen

Hi, i recently bought a new Sony Vaio laptop. Its had a 100gb harddrive, 1gb ram, 1.66 ghz, centrino duo....anywayz it started up amazingly fast. I used an mcafee anti-virus my sckool provided so i could access there wireless internet...1 day i decided that i wanted to use mcafee security center so i deleted my anti0virus and install mcafee security center....my pc then started to crash randomly and my startup got so slow....my startup would delay at the welcome screen and then my wallpaper would appear but it would take like 20 seconds for sthe start button to appear. I uninstalled mcafee and installed zone labs secuirt suite. But my start up still delayed at welcome screen and wallpaper....I did virus scans, spyware and adware scans, defraged and did registry cleanup with registry mechanic....i also use msconfig to reduce amount of programs that started up...i also tried bootvis but nothing is helping...my cold boot is like 2.5 minutes....idk what to do....im thinking about reformating my hardrive...any ideas?