Are you talking about the BIOS password or the Windows password? There are several problems that may be causing this issue.
Firstly, this may be a Windows issue. So you should try booting in Safe Mode or using a Windows installation drive in order to repair your installation. Using the Repair option may fix some errors and it will not harm the stored data.
Option two is an overheating issue. Please make sure that all the cooling fans are clean and that the temperature in BIOS is in normal ranges. BIOS is accessible, right?
Another thing to check is the hardware. Sometimes a problem with the hard drive may cause booting problems. Please check if the hard drive is correctly recognized in BIOS. While in BIOS, confirm that the RAM is listed there with it’s total capacity.