checking pc temperature

I have a dell dimension 9100 and I was wondering how I can check the temperature of the pc. Someone said that I need to go to BIOS, but I tried that. I pressed F2 to get to Bios and I saw no feature where it said the temp of the pc. Im asking this because a couple of days ago my pc was making a beeping sound every 5 minutes. Someone told me that it could be overheating and that this may be the cause of the beeping sound. Also the beeping came from the pc and not the speakers. I shutdown the pc for a few hours and after that the beeping sound stopped. Pc has been working fine when it was beeping so I guess there was no problem. If the cause was overheating then that makes no sense since the dimension 9100 has a btx cooling system. Whats the recommended temperature for a PC?