I have a 500GB WesternDigital Elements external harddrive and recently I plugged it into my computer and noticed the green light on the power adapter didn't light up anymore. I'm assuming that the power adapter failed - is this a fairly safe assumption? I know it COULD be something else, but does this at least make sense to move forward?

Coincidentally, I've been researching new externals to order a 1.5TB because the 500GB is full.

I'm contemplating two options:
1.) Replace the power supply for ~$40
2.) Take apart the external and mount it internally

If it is in fact the power supply it might be the best option to just replace the thing and have 2 externals for backing up data on. But if it turns out to not be the power supply I'm out $40.

I'm not sure how taking apart the external and install the hard drive in a desktop computer would be. Is the harddrive a standard drive? Does it have all the same power cords a normal computer would? If so, I could just install it into my brother's desktop and retreive the data that way (and he'll have an extra 500GB hdd).

Any advice is appreciated, especially any tips installing the harddrive internally.

You should be able to check the power supply by unplugging the supply from the drive, then plug it into the wall. Use a multimeter to see if you're getting the appropriate voltage. If not, then it's fried.

I've never taken apart an external drive so I can't say. I would guess they're just standard drives, but don't know for sure. It might be that they have a different circuit board to interface with instead of standard one that has the SATA/IDE connector on it.

As somebody who has swapped more than his fair share of hard drives, external drives are internal ones in disguise. No problem to put in a box. Some are ide, some are sata, but as long as your plugs look righ it just walks in.

Ckeck the psu first. It could be the disk that's collapsing the power line, and then you'd be putting a short into your box! And plug out, don't just switch off.