Hi Let me start off with my specs Brand: HP Pavillion HPE h9-1185in Phoenix Processor: Intel-i5 (3rd gen) 3450 @ 3.1GHZ Ram: 4 GB DDR3 VGA: Nvidia GeForce GT545 with 3GB video memory Ok so I got my pc around September in 2012 and it was running perfectly back then. All my games were running really smoothly without any noticable lag at all. Up to now I havent upgraded my computer and still have the same specs but when I run games now they start to lag after a few minutes of gameplay and these spikes come and go. Some of my heavily modded games, such as Left 4 Dead 2 wont even launch anymore, where as it ran perfectly on highest settings without any lag at all before. So I have a couple of POSSIBLE culprits which I have identified First of all I noticed that when I play games now( even really low end old games that dont require good specs to run), my CPU's fan starts to spin alot faster and there is a greater humming sound. I am not a tech genius but I googled and found out that this may be a problem with my heat sink. This could mean that my pc is overheating. But I do want to add that the degrade in performance is only there when it comes to games, not when running other tasks in the computer. Secondly there is alot of dust around where I live and it gathers easily. I do regular cleaning of the outside of the CPU and sometimes internal cleaning too. But that didnt seem to fix the problem. Is there a possiblity that dust build up on the RAM card or VGA card could be causing this? Remember only games are affected. My third guess is that it may be a virus of some sort, but that seems highly unlikely since I never turn of my kaspersky internet security, even when playing games. But I did set out to scan my pc but I have a 1TB hard drive and it takes too long. I spent an entire day being stuck at around 5%-10%. I dont even know if its supposed to take that long. The last thing is that my hard drive is almost full. Its 1TB like I said and its down to around 20GB now. Could this slow down my games? I Highly doubt that but im no expert. So yeah this is my problem and I would just like to know what exactly is the problem. I am not experienced with working with internal parts of the CPU and would have to get a technician to solve the problem for me if it is a problem with the hardware. So I would really appreciate any help on this topic. Thanks in advance =) P.S. im new on this forum and sorry if I have posted in the wrong group.