My computer shuts off unexpectedly

I have a Dell Inspiron 4100. I purchased the motherboard and cpu separately from different companies. For some odd reason when I'm on the net or doing some work on my laptop the cpu becomes so active that my computer shuts off instantly. I don't have to do much for the cpu to get very busy in whatever it's doing. I have to be careful using my hotmail account because of this. If I try to select several emails the cpu becomes busy, the fan starts blowing, next thing I know my computer shuts off. I don't know if the motherboard can handle the cpu processing capabilities. I have 512mb memory installed. Though I can put more memory in my laptop it shouldn't be acting like this at all with the memory I have. Can someone help me with this situation? Here are the specs for both the cpu and motherboard.

INTEL PIII PROCESSOR. SL5CL

Processor type: Intel Mobile Pentium(R) III

Part number: RH80530GZ00951E  RH80530GZ009512

Package type: Micro-FCPGA

Processor speed (MHz): 1200/800

Bus speed (MHz): 133

L2 cache size (KB): 512

Core voltage (V): 1.5/1.15

Product stepping: FPA1

CPUID: 06B1h

 

Dell Latitude C610 / Inspiron 4100 Motherboard. Also compatible with Dell Latitude C510

Dell Compatible Part#: 4M984 7U256 4P515 4D845 4P518 2K072 7D845

Supported Processor: Intel Mobile Pentium III up to 1.2Ghz
Number of Memory Slots: 2
RAM Capacity: 1 GB (2x512MB)
RAM Type: PC133 SDRAM
Graphics RAM: 32 MB Onboard
PC Card Slot(s): 2 x Type II, 1 x Type III
Ports: 1 Parallel, 1 Serial, 1 PS/2, 1 VGA port, 1 USB, 1 S-Video
Docking Station: 1 connection for port replicator
Network:  Integrated 10/100 3Com 3C920 RG-45 Network Lan Port
Integrated Audio: Sound Blaster (software emulation)
Audio Controller: Crystal CS4205
Stereo Conversion: 16 bit
Audio I/O: Microphone-in minijack;headphones/speakers minijack
Speakers: Two 4-ohm speakers 1-W (minimum) to 1.5-W
Supported Battery Type: Li-ion, 3,600 mAh
Power Management: ACPI 1.1