Slow PC especially during boot-up?

the one that pops up eh? you've either got no room left on the hard drive, windows needs a bit of room so always try and leave 15gb free. or you've had a pop up saying low disk space and its a virus. run a decent virus checker and adware tool. and delete some stuff off the drive if its near full. use summit like ccleaner to clean the registry as this can get clogged up too.