my pc-xp system-performance has been getting progressively worse. it started with slow operating and then an alarm noise started going off intermittantly. it makes a rythmic high low sound for a while and then goes away and returns again in one hour or two. the sound comes through the speakers and from the case. the computer is acting strange, dropped connections eror4 messages failed downloads(windows update). recently computer would not shut off, so i restarted in safe mode and re loaded xp, problems are the same. i wonder if it is something i can replace or system is going to die. any help would be appreciated.