Overheating, sleep mode and wireless issues-Dell L521x

I recently had to have my L521x's hard drive repaired after it started to fail, and I believe it had to do with overheating. 

Although I do use the laptop for games, it's not its main use. I've experienced overheating both while playing a resource-intensive game and also while just browsing the internet. I usually keep my laptop on a set of four pillars ~1 inch high on top of a desk so it has space for ventilation, but I also use it in my bed. I never leave it on the mattress or covers. The way I hold it is kind of hard to explain, but it always has at least a few inches of space underneath for ventilation. Even then, it gets very hot. 

On top of that, my laptop will not stay in sleep mode with the lid closed. It goes to sleep for a couple of hours or so, then turns back on and runs the hard drive continuously. When I open the lid, the screen turns on directly to the login screen. No loading or anything. 

On top of all that, the wireless connection is basically useless. The two rooms I use the laptop in are probably 10-25 feet away from the router. Both the router and modem are brand new, and my phone and tablets have no problem connecting to the wireless. 

In the closer room, the computer usually can find the network and connect, with full bars. But as soon as I actually try and use it, it drops to 2-3 bars and goes crazy. It will randomly disconnect from the network and say that there are no networks available. When I try and troubleshoot the problem, it resets the wireless adapter. If that doesn't work, the troubleshooter says there is nothing more it can do. Usually if I reset the adapter a few times it will finally find the network again.

In the farther room, it does the same thing except without ever initially connecting at all. 

I've tried everything, from disabling firewalls to disabling the virtual wifi adapters. Nothing has seemed to help. I've resorted to using ethernet cables, with which I've had no issues so far.

So my questions are: Is there any program or anything that could be causing the overheating/sleep mode issues, or is it a hardware defect? And I know that the L521x model has been reported to have wifi issues, does that mean I'm just SOL, or is it a wireless card issue, software problem, etc.?