Is my CPU temperature increase speed normal?

I have a Pentium D 2.8GHz CPU and I am conceed about its temperature. I would leave it off and wait a good day or so (have a nap). I would then tu it on I go straight into BIOS and straight into hardware monitor. It would start at 30-35°C. The fan is then quiet 2100rpm. I stay in the BIOS on the same place and in just 2 minutes the CPU will then reach a temperature of around 60-67°C and the fan will then noise (2800rpm). The system fan still be quiet however. Is this really normal. The BIOS is a very basic BIOS so it doesn't even have support for mouse of fancy graphics so surely it shouldn't be that hot.

When I finally boot into the OS and use it for a bit it restart it and find it is at around 69-70°C.

The room is at room temperature and there is actually a ventilation thing near so it shouldn't be too hot.

• Graphics: ATI RADEON X200 SERIES (INTEGRATED)
• RAM: 2GB
• CPU FAN: Is the the same fan that came with the PC (it hasn't been changed) Simple Acer cooler.

The PC was bought in 2006 so I am not really expecting to function that well but it didn't have these temp changes before.

The system is also kinda dust inside but is that really the problem

Sorry for weird tense at start