Drive not ready problem in windows Xp

ur pc is infected with some virus what av ur using update it perform a full scan

When does it happen? Does it happen at any specific time like when you enter a pendrive?

Your computer seems virus infected. Scan your PC with any free antivirus like Avira or Avast!
Make sure they are updated with latest virus definitions. If they show you are clean scan with a online AV
HouseCall - Free Online Virus Scan - Trend Micro USA