to restart explorer, you could restart your pc.
without restarting your pc: press ctrl + alt + del and bring up the task manager > click the new task button at the bottom of the app tab> type explorer.exe or browse to windows folder and select explorer.exe
to copy/move files around your hdd, you can try explorer alternatives like tera copy or total commander: http://www.codesector.com/teracopy.phphttp://www.ghisler.com/
scan your pc with an antivirus software like mcse, avast or avg and anti spyware spftware like malwarebytes antimalware.
check task manager if your ram or hdd is busy 100%, try to increase your page file size, if possible - add ram.
if your installation is too old, you can reinstall your os or upgrade to windows 7. make sure you back up your data if you do.