Cannot open Windows XP

A sudden problem. On switching on computer, get COMPAQ screen then automatically transferred to page saying Windows did not open successfully and inviting me to open in safe mode; safe mode with networking, etc, with countdown clock. When clock has count down to "0", I then get Windows opening screen with moving dots; then get completely blank screen.

Machine came with pre-installed Windows XP home edition and was my uncle's before he died - he never gave me any CompaQ, windows or other disks - what can I do - I am a little computer illiterate, but can follow clear instructions very well.

Can anyone help?

Thanks

mphillmc