PC not booting past splash screen?

I used to leave my pc on 24/7 but since hydro got so expensive now i shut it down when i leave in the morning and when i go to bed. Lately it has been having problems booting up. Sometimes it will hang for a really long time on the splash screen which gives you options for bios, etc. (like, 4 minutes, where it usually only takes a few seconds) Sometimes it will boot up fine. Sometimes it will boot up, and then my system will gradually freeze up, like, my firefox will get the spinning wheel, then my taskbar, then task manager, and ctrl-alt-delete won't work, and all i can do is press hard reset. the worst of times, it hangs on the splash screen and doesn't boot whatsoever. I have to give it sometimes multiple hard resets before it will finally boot.
I am concerned. I am thinking that since there are issues actually booting past the mobo, and the system sometimes freezes, I am concerned that there may be a problem with my C: HDD?

That being said, I have both Win 7 and XP on this pc on different drives, and when it freezes, it doesn't even allow me to get as far as to select what drive to boot into, which it will always do after the splash screen.

Does anyone know what could be going on?

Thanks.

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Operating System
Windows 7 Ultimate (x64) Service Pack 1 (build 7601)
Windows XP SP3

Processor
3.20 gigahertz Intel Core i5-3470
128 kilobyte primary memory cache
1024 kilobyte secondary memory cache
6144 kilobyte tertiary memory cache
64-bit ready
Multi-core (4 total)
Not hyper-threaded

Board:
Gigabyte Technology Co., Ltd. H77M-D3H
Bus Clock: 100 megahertz

BIOS: American Megatrends Inc. F5 03/29/2012

RAM:
Slot 'ChannelB-DIMM0' has 8192 MB

Display:
NVIDIA GeForce GTX 660 [Display adapter]
Samsung SyncMaster [Monitor] (24.0"vis, s/n YCUYHVDZ702086, July 2010)

Audio:
NVIDIA High Definition Audio
VIA High Definition Audio