My computer becomes slow for short periods?

If this happens only at start up, then you have too many programs trying to start at the same time, so after you start it up and get thru the "slow" time, go to start>run>msconfig>enter. In the screen that comes up you will see start up selection, highlight the selective start up button(if not already selected). Then click on the startup tab at the top and go down the list and un-check files such as google update or any other auto-update files like itunes, microsoft office ect(they dont need to check for updates when starting, they will update when you use them). When your done, click apply then ok and you will get a message to restart, go ahead and restart. now the start up should be a little faster, if not, you can try cleaning the registry with a free program called "free window registry repair" download and install/run it.

It can be System Restore (turn it off and delete the backups), an anti-virus program or some sort of auto updates.

Hit control-alt-delete and start Task Manager to see what processes are running and what resources they're using.

It can also be increased virtual memory usage from so much software running and so many bloated Windows updates. You solve that by adding more RAM.

i had a toshiba laptop that did the same thing i fixed it be re installing the operating system

Try cleaning your registry that should help