Fine startup but slows down?

Hello I'm not sure that this is exactly a windows problem but i dont know what else it could be. I'm not exactly sure when it started but it's been a couple weeks at the least, when I start up my laptop it runs fine but it usually varies in the amount of time but after about an hour or so it slows way, way down to the point i can't open the Ctrl-Alt-Del menu, the computer freezes and unfreezes and i just have to restart and then it's fine again for a while, i have done full scans on malwarebytes, avast and ad aware none find anything, i have used CCleaner and Defraged my system, I've turned off all unnecessary start up programs and tried a SFC /SCANNOW in cmd, and nothing is working the problem still persists i have run out of ideas so any help would be great.

here are my system specs i also have a 298 GB hd of which i have 92 GB free

OS Name Microsoft Windows 7 Ultimate
Version 6.1.7601 Service Pack 1 Build 7601
OS Manufacturer Microsoft Corporation
System Name TERRYSPC
System Manufacturer Gateway
System Model P-7805u
System Type x64-based PC
Processor Intel(R) Core(TM)2 Duo CPU P8400 @ 2.26GHz, 2267 Mhz, 2 Core(s), 2 Logical Processor(s)
BIOS Version/Date Phoenix Technologies LTD 9C.23.00, 10/1/2009
SMBIOS Version 2.5
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Hardware Abstraction Layer Version = "6.1.7601.17514"
Time Zone Central Daylight Time
Installed Physical Memory (RAM) 4.00 GB
Total Physical Memory 3.99 GB
Available Physical Memory 2.50 GB
Total Virtual Memory 7.99 GB
Available Virtual Memory 6.33 GB
Page File Space 3.99 GB
Page File C:\pagefile.sys