A defragger may fix a slow PC.
A great one, being Auslogics Disk Defrag which is free.
Another nice but free tool, but doesn't seem to be updated anymore, is Easy Cleaner, made by someone called ToniArts.
I don't trust CCleaner to be honest.
Abit IP35 Pro / Q6600 G0 / Zalman 9700 / 8800GTS 640mb / 4x 2GB Corsair XMS / X-FI Xtreme M / 1x 1TB / Antec 900 / Logitech Z-5500 / Samsung 20inch