PC Lag Spikes

Recently I have been receiving strange lag spikes in general use of my PC. These spikes occur when using Google Drive, playing games or doing whatever. A lot of the time my PC is very fast and responsive, however every minute or so everything slow down for about twenty seconds; typing becomes laggy, games freeze up etc. I do not know the cause of this issue and any help would be extremely appreciated.

Thanks, Isaac

PC SPECS:

Summary
Operating System
Windows 8.1 Pro with Media Center 64-bit
CPU
AMD Phenom II X4 960T
Thuban 45nm Technology
RAM
16.0GB Dual-Channel DDR3 @ 669MHz (9-9-9-24)
Motherboard
ASUSTeK Computer INC. M5A78L-M/USB3 (AM3R2)
Graphics
S240HL (1920x1080@60Hz)
1024MB ATI AMD Radeon HD 6670 (ATI AIB)
Storage
931GB Seagate ST31000528AS ATA Device (SATA)
Optical Drives
ATAPI iHAS124 B ATA Device
Audio
VIA High Definition Audio

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