Emma
We have been trying to find out the answer to that question for 5 weeks. We have not found anything to say your computer is infected but, however much you scan, the tools you use are not infallible. Neither can we ascertain why the Windows Security Center fails to detect Panda.
You need to decide:
- Whether to live with the problem.
- Change your anti-virus software or
- Reinstall Windows retaining Panda.