my dell desktop has slowed down significantly all of a sudden. i think its perhaps cos the juice on the cmos battery's run low. could this be the issue, since all other variables have remained unchanged?
No, a dead CMOS battery would not cause your system to slow down.
Most likely, you have caught a virus, some spyware or it is overheating.
Open the case and use a can of compressed air to clean out the dust bunnies from the heat sinks (and every where else).
After that is done, install, update and run AVG Free to see how much junk is slowing you down.
Finlay, post your full system specs, CPU and GPU temps (use Coretemp or Realtemp for the CPU, GPUz for the GPU) and more detailed descriptions of your slow downs (is it slow booting, in a specific application, after running for a length of time, etc.).