My PC regularly fails to find key components when it boots up.
The problem first showed itself when I installed new software from a CD. The installation required a re-boot, but when re-boot took place the installation did not complete automatically. When I looked at "My Computer" I found the DVD drive was not showing up. I had to switch off - leave it for a while and reboot later. Occasionally the PC can't locate the Hard Drive and doesn't boot at all.
These problems only occurred when PC had been running for a while and I had to re-boot (eg during software installation.) However I recently went wireless and now I find that the computer often fails to find the wireless network connection when I first switch on. I have to reboot once or twice for the PC to find the wireless card. My feeling is that this is a hardware problem. All components are firmly connected.
My PC is a no-brand tower system from a independent computer store with an i5 processor, running Windows XP.
Sounds more like a software issue if it happened after you installed a program. Have you tried a system restore or uninstalling the new software program?
If your system was working well before you installed that software, I'd try the above.
If you were facing these problems before that, it could be a faulty PSU. I've had similar problems, DVD drive / HDD wouldn't show up... replacing the PSU cleared it up.
Please post your system specs, it might shed some more light...