emmie - when you've done that it's worth using the "error checking" option on the tools menu. You disc is quite old and that option will sort out any errors on it and, if you tick both options, will replace any dodgy segments of disc it finds with spare ones that are available just for that purpose. If there are dodgy bits of disc the machine persists in trying to read them and the delay can be noticable; if you error-check it can, effectively, speed up the disc.
Just be warned that error-checking the C drive cannot be done whilst you are using the computer and can take a long time, so you have to let it do it next time you restart. The best way is to ask for the check to be done then, after you power-off your machine for the night, restart it and go to bed; by morning it will have finished.