Windows 7 acer pc wont start up and system repair wont do anything?

ok so this is a very detailed version of what is happening, when i start up my acer computer with windows 7, it brings up a black screen, it asks to start windows normally or to launch startup repair. When i click on start windows normally, it will show the starting windows screen for about 30 seconds then... show more ok so this is a very detailed version of what is happening,

when i start up my acer computer with windows 7, it brings up a black screen, it asks to start windows normally or to launch startup repair. When i click on start windows normally, it will show the starting windows screen for about 30 seconds then restart. When i click on startup repair, it goes to the startup repair screen then says startup repair cannot repair this. I've sent it before and waited for days and nothing happened. After I've click to send or not to send, it brings me to another screen that says "If you have recently attached a device to this computer, such as a camera or portable music player, remove it and restart your computer. If you continue to see this message, contact your system administrator or computer manufacturer for assistance." Click finish to exit and shutdown your computer. It gives me the options of viewing diagnostic and repair details, or view advanced options for system recovery and support. When i click on view diagnostic and repair details, it shows that i have one root cause which is that "Startup Repair has tried several times but still cannot determine the cause of the problem." When i click on View advanced options for system recovery and support, it asks to select a keyboard input method (US) and then goes to another page titled "System Recovery Options." It says to choose a recovery tool and also says "Operating system: Windows 7 on (D:) Acer" It gives me the options of Startup Repair, System Restore, System Image Recovery, Windows Memory Diagnostic, Command Prompt, and Recovery Management. It also gives the options to shut down or to restart. When I click on System Restore, it would run for days and won't do anything. Can somebody help me fix this so i can start my computer? Can you do it in step by step details. Sorry for the long paragraph but i just wanted to explain everything in the most detail i could.
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