First, stop trying to use that computer. AMD chips overheat easily and they can be permanently "cooked".
Most of the newer mobos *should* shut down if it senses the cpu fan isn't turning. It monitors the the pins where the cpu fan is plugged into the mobo. If just the fan is cooked, and your mobo is "smart", you should be ok right now. That would be why it pauses for a second before trying to boot again. If the power header or some other part of the board is fried, then you're SOL.

Any fan will work as long as it can be attached to the mobo pins and aimed at the heatsink. If you have an old case fan, swap the plug leads and you're ready to go. Otherwise it'll cost you ~$8-$12 wherever computer stuff is sold nearest you. Be careful swapping the cpu fan because the AMD chips do chip/crack easily and then you'd
really be hating it. Where are you located? There might be someone local with a spare fan. I don't think I have anything under 120mm, but I'll check in the AM. Measure the length of one of the sides of the fan (in mm) and post it. The same size fan will bolt up easier, but anything can be used in a pinch.