hi Zajo,
this type of problem requires us to do somewhat of a trial-and-error deductive troubleshooting.

1. check hard disk (and file system) that contains your windows drive
2. check RAM


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Check the hard disk:

If you have second computer that you can use to attach the faulty computer's hard drive (using an enclosure OR by plugging it into an available ide/sata port). With the hard disk from the faulty computer connected to a working windows computer, perform a check disk on that drive. If there are any file/sysutem errors on that drive, it can be fixed and it should boot after.

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Check the RAM

with the hard disk out of the faulty computer, check the RAM using "Memtest 86+" (you can use a floppy or CD that has Memtest 86+").

in detail:

1. determine if your computer has only 1 stick of RAM, or 2 sticks of RAM
2.1. if computer has only 1 stick of ram, then proceed to use Memtest 86+ to check your ram

2.2 if computer has two sticks of ram, then detach 1 stick and test with Memtest 86+ using only that single stick of ram. After passing memtest 86+ for at least "pass 4", test with the other stick of ram.


***these are my quick advice on how you can test this problem. post here if you have any questions about the said procedure or program (like Memtest 86+) goodluck