Having multiple errors with XP Pro

My computer started restarting its self and then there would be a box saying ""your computer recovered from a serious error", do you want to send a report", which i did. Now when it restarts its self i no longer get the error box. Some times after it restarts on its own, nothing works and i have to manually shut it off.
After restarting it, every thing seems to work fine. It usually restarts when i'm not using it. Its also starting having this whirring sound, like an airplane taking off. It gets louder and louder and will stay that way for awhile, than it gets quiet again. This is a refurbished computer my dad bought for me online from a walmart site.
I see in my system info that it says i'm running Microsoft Security Essentials, the only place on my computer that Microsoft Security Essentials is, is in the recycling bin. I had trouble with it and uninstalled it awhile ago. It is an HP Compaq computer.

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows XP Professional, Service Pack 3, 32 bit
Processor: Intel(R) Pentium(R) 4 CPU 3.00GHz, x86 Family 15 Model 4 Stepping 3
Processor Count: 2
RAM: 1015 Mb
Graphics Card: Intel(R) 82945G Express Chipset Family, 128 Mb
Hard Drives: C: Total - 76316 MB, Free - 55092 MB;
Motherboard: Hewlett-Packard, 09F0h
Antivirus: Microsoft Security Essentials, Updated: Yes, On-Demand Scanner: Enabled