Suggestion 1: Run your Anti Virus scanner. Also run several Malware scanners, like Malwarebytes, Superantispyware, spybot. There are many others.
Suggestion 2: Start > Run > msconfig. Go to the Startup Tab and uncheck any application you do not really need to load at startup. Reboot.
Reply & Request-I have already done the scanning with avast. also have run the msconfig and uncheck the unnecessary applications but still the same problem. exactly after first screen of windows xp screen goes blank for long time(3 minustes approx) after that welcome screen appears and when i log on in my profile the cursor(with sign of executing tasks) remain at the welcome screen for 4 approx minutes.when it goes in it takes 2 minutes to be able to start working.
Would have been nice to know what you had done previously to troubleshoot the issue. But, don't just rely on AVAST to solve all virus malware issues. Give malwarebytes a try. And since you are on XP run rootkitrevealer to see if it detects anything.
Also, what are your system specs ? Specifically RAM and what is in your startup ?