Suprisingly enough Hdds do thro out alot of heat and with this weather I'm not suprised that the PC is running hot.
MMB5 motherboard monitor will check out the temperatures for you.
If it is warm try
1. good air space and flow round machine (off carpet))
2. direct a houshold fan onto your PC
3. a couple of extra case fans (£1.99) rear blowing out front sucking in.