Hi there Samuel_11,
It seems that the HDD is failing. Have you tried something simple as just using different cables? In case you haven't, you can try that.
Have you backed up all your data? In case you haven't, and the drive prevents your system from booting properly, you should either use some data recovery tool for DOS mode or get an SATA to USB adapter+power source and attach the drive externally.
For example, you can boot up Ubuntu from a flash drive or a CD and try to access the drive: http://www.tomshardware.co.uk/forum/267999-32-recover-data-mode
After you've recovered all your data, you can test the drive with a brand specific testing tool. For most of them, there is a DOS version as well.
Hope this will help,