Restart problem with PC

I have a Pentium II 233 Mhz Pc with the following specifications-32 MB SD RAM, Intel 440LX motherboard with 512 KB LII cache, 4.3 GB Seagate Hard Disk, 200W Switch Mode Power Supply. In the last few days, my PC just restarts on it own without any apparent reason. It does not power off and then power on again but just restarts on its own just like when you explicitly hit Ctrl+Alt+Del The PC does not remain powered on for more than 5 minutes at a stretch without automatically restarting. In the 5minutes that it does stay powered on, it functions normally. What could be the problem??