I'm a touch 'old school' when it comes to connections inside or outside computers. I had the pleasure of sorting out a PC that belonged to the parents of a dear friend over the weekend, and all seemed to be going well.
They had a rather dodgy version of Windows 7 installed and Microsoft Security Essentials was complaining that it might not be 'genuine software'. I elected to remove this and install Grisoft's excellent AV product called AVG. All was going well, until I went to reboot. I had removed a game CD from the CD drive prior to rebooting.
System rebooted and promptly told me there were disk errors - press Ctrl Alt Del to restart. Each restart then displayed differing errors, namely - slight corruption on the BIOS screen, failure at different points of the boot process, and oh dear, it was all going wrong for Johnnyboy at that point.
After checking the obvious, and then booting into my OS on my USB flash drive, all seemed OK. I normally carry around an install of Puppy Linux 4 OS to assist me in case Windows can't boot. And that happens rather too often for my liking.
Opening up the case revealed a rather warm PC. The power supply unit (PSU) was in the opposite corner of the case to that which I was expecting, and consequently covered most of the motherboard connections for the PC/case. I hadn't been able to figure out why I wasn't able to boot up after simply removing the CD.
After a bit of prodding around and checking, and then reseating cables, I discovered the cause. The CD drive had ejected rather forcefully (a good example of this effect would be a slide hammer) and in doing so had made the connection for the SATA HDD lose partial connection with the motherboard. I suspect that this was mainly due to the heat build-up and subsequent heating/cooling effect when the PC was switched off and on, and therefore making the connections possibly somewhat looser than required.
IDE connections are very firm and secure, but hard to work with in the confines of a PC case. SATA cables are great, and easy to work with but the less than solid connection has always concerned me. If you ever have troubles booting your PC after installing a new HDD, then I would certainly recommend checking the SATA cable connections as a first port of call.