Hi I've been frustrated with my pc performance of late. From lagging browsers to lagging single player games, unfortunately I don't have the biggest hard drive and well I did a dumb thing and split it into two. I'm not playing games that require an immense amount of space though. I have run scans and I do clean ups etc, yet I experience severe spikes and lag at times, this happens on old games like Diablo2 or Sims2, a few months ago I was playing games like Left 4 Dead and Crysis without any problems. What is causing my machine to run sooo slow? Think it's time for a new pc :/?

My pc specs are:
Mainboard : Gigabyte G31M-S2L
Chipset : Intel G31/G33/G35
Processor : Intel Pentium XE 820 @ 2800 MHz
Physical Memory :4096 MB (2 x 2048 DDR2-SDRAM )
Video Card : Nvidia Corp GeForce 8500 GT
Hard Disk : Maxtor (160 GB)
Operating System : Microsoft Windows XP Home Edition 5.01.2600 Service Pack 2