Too little storage, too slow.
The upgrade went well, except for two snags.
One was a bent pin on the motherboard power connector. Most likely, it was unbent a little bit when unplugging the power connector, then got really bent trying to plug it back in, but it was fixable with some pointy pliers.
The second was forgetting to put the fan back in, and only noticing after having stowed everything away again. Easily fixable, just annoying.
Check the power connector pins before attempting to re-insert the motherboard, and straighten the pins if necessary. Also, be careful plugging it back in, don't force it if there seems to be too much resistance.