1. The most usual cause of this sort of behavior is what is called thrashing. This refers to the excessive use of virtual memory paging to compensate for having insufficient real physical memory to hold all of the applications and data that are in use. Especially if you are using many applications or large files, and also if there isn't a great deal of real memory in the PC, the operating system will have to move some of the contents of memory to the hard disk when it runs out of space. Then, when you need whatever was swapped to disk, it is loaded and something else is swapped to the disk. This is a supply and demand situation; the only way to resolve it is to increase the supply of real memory, or reduce the demand created by applications and data open simultaneously.
2. Make sure that it is not a "Scheduled Task" that is starting up.
3. Check if there is an Anti-Virus software that starts up.
· Upgrade the amount of physical memory in the system, especially if you don't have enough memory in the PC for optimal performance based on your operating system.
· Reduce the number of applications running in the system, and reduce the number of data files you have open. If you are finished using something, close it to free up memory for programs you are still using.
· Cut down on the number of "toys" that load automatically when the system starts up. The more automatic utilities, scheduling reminder programs, memory-resident tools and other gadgets that load when the system starts up, the less memory that is available for "real" applications, and the more likely that thrashing will occur.