Les - if you can put on a plug and change a fuse there's no reason not to guddle in the innards. It's simpler than it was 10 years ago. All the cables and sockets are keyed or color-coded so it's hard to plug things in the wrong way round unless you force it. Often the problem is a lose cable or a bad connnection. Pull it out, give it a spray of circuit cleaner & a wipe and put it back. Solves a lot of hiccoughs. So does a whoosh of canned air to blow out the dust bunnies.
Having said that, you DO need to be careful and check what you are doing. A marker pen and a notebook help. Commonest problem is to take out/insert something and unseat a nearby connector or dislodge a jumper. If you do something and it hangs, that's often the problem. Trouble is, folk then start playing around with the BIOS or the OS, which is FAR more likely to get you into terminal trouble and end up with data loss and a reinstall.
Best defence? Like aircraft I guess. Get familiar with your system and RTFM. Backup your Registry often [
http://support.microsoft.com/default...;EN-US;q139437] Ghost your main drive to a removable HDD and keep it in the woodshed. Takes 15 minutes. Repeat regularly and esp. before you install that new game or latest update.
It's hard to fry a PC in hardware, easy to stuff up the system in software.