how to remove this pop up?

To resolve the issue, use one of the following methods:
Insert a removable disk in the removable drive before you start the computer.
Change the drive letter assignment for the removable drive to a letter other than C.

To change the drive letter assignments in Windows XP, follow these steps:
Log on to the computer as Administrator.
Insert a disk in the removable drive.
Click Start, right-click My Computer, and then click Manage.
Click Disk Management.
Right-click the partition, logical drive, or volume that you want to change, and then click Change Drive Letter and Paths.
Click the removable drive, click it, click Change, click the drive letter that you want to use, and then click OK.

Download and install Malwarebytes anti malware tool (free version)  from
http://download.cnet.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?part=dl-10804572&subj=dl&tag=button and perform a quick scan. Once the scan is completed, select show results and remove all selected infections.

ok