Hello Putspa,
Thank you for providing us the opportunity to assist you.
As per the issue description you are unable to perform Satrtup repair on our computer and you don't have the installation disk too.
First disconnect any external devices connected to the computer except the mouse and keyboard.
This error usually happens if the hard drive is not getting detected by the operating system or due to bad hard drive.
First check if all the physical connections to the computer are set correctly. If it is a laptop remove the laptop battery, wait for 5 minutes and then connect back the battery, check if it works.
I would suggest you to boot the computer in safe mode and see if you are able to boot to the desktop.