Hi Melody,
That is a standard message that has been there for as long as I can remember. If you have not normally seen it before there is a setting you can change on WinMX to 'surpress' those warnings and maybe you have ticked or unticked it. Its in Settings > File Transfers > Look on the right at the last two choices on the box.
Computer crashes can be caused by many things. The most common im aware of for your entire PC to crash and shut down is a processor that is over heating. Im sure there are others on the site that can offer you more advice about that and how to check it. If you suspect this you may want to remove the side of the PC and make sure your fans are all running while the PC is on. Esp the one on the actual processor. If they are running ok, try leaving the side off for a while and see if it continures.
You mention the -c and that is no longer working. The only way to filter fakes files out of yoru searches that can cause WinMX to crash is by using the WinMX Group Patch. If your update bar doesnt say Patch Operational in the top above Networks then be sure to reinstall from here:
www.winmxgroup.comIf your WinMX is the only thing crashing and your not sure what patch you have then reinstall from that site. Remove any incomplete files you have setting in transfers especially ones with 0% and then refind sources.