Win 8 slows down dramatically after a week repeatedly

After a week of using both on and offline WIN 8 like clockwork slows down after a week, there are have run multiple virus and malware checks and nothing, task manager shows normal with only 28% memory use, programs running are minimal, no unusual hard disk accessing, defrag is run every two days and again performance falls dramatically both online and offline.

The only way to get performance back has been to do a system REFRESH, but once a week is NUTS!

This is a Win8 certified Gateway laptop with 2.20 ghz Pentium processor and 8 gigs of ram.

Anyone else with similar problem or solutions, please think before responding.

Question - is the laptop shut down and restarted at any point between the first day and when the issue occurs? Is it restarted? Or is it put to sleep or left running? I'm curious the exact steps that happen to get to this point - if it is shut down / rebooted and not restarted, or is left running for that time, the behavior sounds like a memory leak of some kind. It'd be interesting to know the exact details of what the system is doing from day one to the time the problem occurs.