Processor speed slowing down

I have a Pentium 3 700MHZ processor. But everytime I run DirectX Diagnostic
it always says I have a 550MHZ processor. Do processors just lose speed after so many years? Any information would be helpful.

No, but your computer could underclock them which basically slows them down below actual speed.

Is there a way I can get it back to the regular speed?

Check your BIOS and make sure your FSB is set to the right freq. and/or the CPU multiplier hasn't changed. I'm not sure what they are for a P3 700Hz, but a guess like 64MHz and a multi of 11 gives 704MHz, so it should be numbers similar. FSB X CPU multiplier =700Mhz.

Aslo check your temps, CPU's will automatically clock down if they are overheating. Clean the HSF of dust, debri and small cats and dogs. Use Everest Home Edition (motherboard tab) to check temps.

if it is a desktop, then it should run at it's full speed all the time.

if it is laptop/notebook, then Intel SpeedStep will downclock it to save energy. some laptops will allow you to disable SpeedStep.

How do I check if my FSB is at the right frequency?