When PC's first start up, they have certain jobs to do, las well as booting the operating system, they also have to check for updates, (windows, anti-virus & others) a virus scan may run every time if using AVG free version. Make sure disk is defragmanted as least once a week. Unistall any none used programmes, as these will all conrtibute to a system slowdown...you may even have a virus infection..!!
lesthered, November 2008