How do I stop my computer from freezing after it goes idle?

I've been having serious issues with my computer. I've recently downloaded Microsoft Security Essentials which found several exploits, a few trojan/trojan downloaders, and even a malicious program. (Power Regulator or something like that) I've quarantined all that, and thought it would be fine. However,... show more I've been having serious issues with my computer. I've recently downloaded Microsoft Security Essentials which found several exploits, a few trojan/trojan downloaders, and even a malicious program. (Power Regulator or something like that) I've quarantined all that, and thought it would be fine. However, my computer keeps freezing. 90% of the time it's after it's been left idle for 10 minutes or longer. Rarely, but on occasions it will freeze while in use. I'm also getting a double beep on start up. I also ran a diagnostic tool I found, and it says that I need to check the cord to my C: drive. However, Chkdsk said my C: drive was fine. I'm really at a loss for what to do.

System Specs:
Operating System: Windows XP Home Edition (5.1, Build 2600) Service Pack 3 (2600.xpsp_sp3_gdr.100427-1636)
System Manufacturer: MSI
System Model: MS-6712
BIOS: Version 07.00T
Processor: AMD Duron(tm), MMX, 3DNow, ~1.8GHz
Memory: 1280MB RAM
Page File: 821MB used, 1079MB available
Windows Dir: C:\WINDOWS
DirectX Version: DirectX 9.0c (4.09.0000.0904)

Video Card:
Card name: Diamond S9250 PCI 256 DDR
Manufacturer: ATI Technologies Inc.
Chip type: RADEON 9250 AGP (0x5960)
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