Booting fails first time everyday

I recently installed Windows 7 and started facing a weird problem from and 2nd or 3rd day. First time when I start the PC on the day the startup fails and windows complaints the last shutdown was not proper or some driver has shut the system down automatically in order to prevent data corruption. After 3 or 4 (sometimes even 7,8) attempts or after starting in safe mode I'm able to start the PC and it runs like a dream for the rest of the day. If I try to restart it during the day I don't face any trouble at all. And the sad old story begins on the next day. I looked at the system logs and it complaints of a "Kernel power" problem. Searching for windows online help hasn't produced any useful info. Could someone please help providing some bright ideas about to how to solve this issue?
I have changed the system clock now to see whether it changes anything or not.

OS : 64 bit windows 7
Processor : Intel Core 2 Duo
Motherboard : Gigabyte

Thanks for the reply. First when I tried to repair I keep keep getting BSoD. As usually I managed to boot somehow, booted with the installation disk and chose auto repair. It said no problems found. Then I used the command prompt and the "bootrec \fixmbr" seems to work find. But "bootrec \FixBoot" complained with a message "The volume does not contain a recognized file system.". However I can see the C: drive but there are no "boot" directory under it.

I have done it. Windows reported some problem that some of the free disk space has been marked as allocated and it corrected it automatically. Do you think this is good enough to fix the problem?
As this problem either (mostly) happens after the next day or when restarting after a long time I'm not sure what is going to happen. I'll check it and share with you the status. Thanks a lot for your help sofar.
Also, out of curiosity, do you know how it works, if I keep restarting it immediately or after 30,45 mins, 1 hour etc. In that case it starts up without any problem. But suddenly (mostly next day) it sucks.

jacobselvin said:

Thanks for the reply. First when I tried to repair I keep keep getting BSoD. As usually I managed to boot somehow, booted with the installation disk and chose auto repair. It said no problems found. Then I used the command prompt and the "bootrec \fixmbr" seems to work find. But "bootrec \FixBoot" complained with a message "The volume does not contain a recognized file system.". However I can see the C: drive but there are no "boot" directory under it.

Ummmm... not to be tooo picky but ...

It's bootrec /fixmbr
not bootrec \fixmbr

And yes, it does matter

On other thought... Shut things down normally tonight, so that you're likely to have the problem first thing tomorrow... but in the morning don't boot the OS go straight into your BIOS settings and see if they've changed... It could be something as simple as a bum CMOS battery or a BIOS setting error.

Yesterday I shutdown my PC at 23:00 and restarted it at 1:30 AM and it started without any problem. I went to sleep and checked it in the morning around 7:30 and it fails to boot again. I checked the BIOS settings straight away. I could see some parameters being changed (booting sequence, usb keyboard disabled etc). However my system clock is running perfectly. Is this possible? Is there any separate battery for clock?