Si me podéis dar una solución, os dejo el log de ASWmbr, gracias.
aswMBR version 0.9.9.1532 Copyright(c) 2011 AVAST Software
Run date: 2012-02-14 15:08:18
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15:08:18.825 OS Version: Windows x64 6.1.7601 Service Pack 1
15:08:18.825 Number of processors: 2 586 0x603
15:08:18.825 ComputerName: PORTÁTIL-HP UserName: Leticia
15:08:20.323 Initialize success
15:08:20.401 AVAST engine defs: 12021400
15:08:22.991 Disk 0 (boot) \Device\Harddisk0\DR0 -> \Device\Ide\IdeDeviceP0T0L0-0
15:08:23.006 Disk 0 Vendor: WDC_WD5000BEKT-60KA9T0 01.01A01 Size: 476940MB BusType: 11
15:08:23.053 Disk 0 MBR read successfully
15:08:23.053 Disk 0 MBR scan
15:08:23.053 Disk 0 Windows 7 default MBR code
15:08:23.069 Disk 0 Partition 1 80 (A) 07 HPFS/NTFS NTFS 199 MB offset 2048
15:08:23.084 Disk 0 Partition 2 00 07 HPFS/NTFS NTFS 455382 MB offset 409600
15:08:23.131 Disk 0 Partition 3 00 07 HPFS/NTFS NTFS 21254 MB offset 933031936
15:08:23.147 Disk 0 Partition 4 00 17 Hidd HPFS/NTFS NTFS 104 MB offset 976560128
15:08:23.162
15:08:23.162 Service scanning
15:08:25.143 Modules scanning
15:08:25.143 Disk 0 trace - called modules:
15:08:25.689 ntoskrnl.exe CLASSPNP.SYS disk.sys hpdskflt.sys ataport.SYS PCIIDEX.SYS hal.dll msahci.sys
15:08:25.705 1 nt!IofCallDriver -> \Device\Harddisk0\DR0[0xfffffa8004689060]
15:08:25.705 3 CLASSPNP.SYS[fffff8800161743f] -> nt!IofCallDriver -> [0xfffffa8004688880]
15:08:25.721 5 hpdskflt.sys[fffff880019bc189] -> nt!IofCallDriver -> \Device\Ide\IdeDeviceP0T0L0-0[0xfffffa80045fa680]
15:08:26.875 AVAST engine scan C:\Windows
15:08:29.085 AVAST engine scan C:\Windows\system32
15:10:11.267 AVAST engine scan C:\Windows\system32\drivers
15:10:18.895 AVAST engine scan C:\Users\Leticia
15:14:25.670 AVAST engine scan C:\ProgramData
15:16:12.278 Scan finished successfully