Might sound a little trite, but your comment on high CPU cycles might be something I have come across a number of times, takes a little time to investigate but check your heat sinks on both the CPU/GPU and chipset, also that any fans are working, if there working, clean and free of dust and dirt not a problem, but if blocked or partially obstructed they may work OK while the comp is not under load but as it loads up or after a long period of running the heat build up can often mimic high process loads and cause a comp to slow to a crawl.