My PC is older-Dell dual core Intel with XP. When booting, there is a "choose OS" page that times out 30 seconds. However, it suddenly began taking a very long time-I could see the timer was sluggish, so using a stop watch, I checked the interval between seconds...it's taking about 7 seconds to count down ONE SECOND on the system clock! Needless to say, it is also now running very slow in general. How can I fix this?