If Panda didn't find any security threats, it means the problem with errors is caused by something else. Use CCleaner to clean the registry files and any other obsolete entries. This step will take care of the slow performance issues.
Once you have finished the job with CCleaner, temporary turn off any antivirus solutions (Panda Internet Security) then scan your computer with Combofix.
Visit the website and download it through BleepingComputer. Scan the computer and you will see that Combofix will wipe any threat from your computer if Panda failed to do it.