Windows 7: My windows 7 problem

Here is my problem
my windows 7 wont start sometimes it hangs then when i restart the system using reset button the bios system wont start i mean the startup screen showing all the info about bios wont show up so i will restart the system again using reset button to show it up then it will start normally i dont know why it reached this kind of problem this is a new and fresh installed PC with win 7 and no programs have been installed yet only basic like ms office
i tried changing the Bios battery too does it mean that i need to buy a new one ?

Run a thorough AV scan
Download and scan with malwarebytes. Lets rule our a possible virus or malware.
http://www.malwarebytes.org/mbam.php

kk i'll try a scan

If the scan is negative report back, we can take other steps.

Malwarebytes' Anti-Malware 1.46
Malwarebytes

Database version: 4513

Windows 6.1.7600
Internet Explorer 8.0.7600.16385

8/31/2010 8:13:37 AM
mbam-log-2010-08-31 (08-13-37).txt

Scan type: Full scan (C:\|)
Objects scanned: 234695
Time elapsed: 40 minute(s), 20 second(s)

Memory Processes Infected: 0
Memory Modules Infected: 0
Registry Keys Infected: 0
Registry Values Infected: 0
Registry Data Items Infected: 0
Folders Infected: 0
Files Infected: 0

Memory Processes Infected:
(No malicious items detected)

Memory Modules Infected:
(No malicious items detected)

Registry Keys Infected:
(No malicious items detected)

Registry Values Infected:
(No malicious items detected)

Registry Data Items Infected:
(No malicious items detected)

Folders Infected:
(No malicious items detected)

Files Infected:
(No malicious items detected)

shows its clean

OK great. Lets see if this is software problem. Boot in safe mode, is the problem the same?

ok done booting with safe mode it seems normal for me nothing unusual
this error i mentioned above in 1st post is like a weather sometimes it pops up sometimes it won't should i consider changing hardware already ?

No, I do not think that it is hardware but, lets wait. If it seems ok in Safe Mode, but we did not really give it a chance, start in clean boot. If computer works ok, for a while, I will show you how to fix it.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7

it seems ok i followed the steps in the site you posted from MS i printed it so i can follow it no signs of errors
i also forgot to mention
the first time i opened my pc this day there is no info of the bios then i rebooted and there was something showing up and it seems that its only the Logo fo the manufacturer (i think) of the bios American Megtrands thats all after it the above post error followed
could it be the bios is damaged as theres no software error ...

Lets try to do this in an orderly fashion, so it comes out right.
You said that the problem does not always happen. So use the clean boot for a while. If you think that you have passed the usage required to have the problem occur, restore the services a few at a time as shown in the Clean Boot bulletin. Then you will know the exact cause.