Anyone know whats wrong with my computer?

well that's not much to go on but it sounds like it may be heating up. Check your fan to see if its turning or restricted by dust and dirt. If the air flowing out is extremely warm there is a lot of heat building up. Open the case and see if there is a lot of dust inside. Particularly around the CPU. There will be a fan and heat sink on it. Look for dust clogging the fins on the heat sink. If the case fan isn't running you may have to replace the power supply (generally the fan is in it) or IF YOU ARE QUALIFIED you could replace the fan in the PS unit. (Use extreme caution there can be hazardous voltages there even after shutdown). All this relates to a heat issue that would be recognized by the fact that your system seems to be locking up after operating for a period of time. It can be other things too. lets start with this.