Why my avast keeps shutting down ?

1) Firewall
You are either using no firewall or XP's firewall. You may enhance your protection by installing a firewall with outbound protection like PCTools, Agnitum Outpost or Online Armor.

(2) Fix these entries
You may fix this entries by scanning with HJT then ticking the box beside them and select, "Fix selected entries"
Regarding toolbars, you may delete these entries if you wish since these are commonly unnecessary.

- R3 - URLSearchHook: (no name) - {E312764E-7706-43F1-8DAB-FCDD2B1E416D} - C:\Program Files\pdfforge Toolbar\SearchSettings.dll
- O2 - BHO: pdfforge Toolbar - {B922D405-6D13-4A2B-AE89-08A030DA4402} - C:\Program Files\pdfforge Toolbar\WidgiToolbarIE.dll
- O2 - BHO: (no name) - {E312764E-7706-43F1-8DAB-FCDD2B1E416D} - C:\Program Files\pdfforge Toolbar\SearchSettings.dll
- O3 - Toolbar: pdfforge Toolbar - {B922D405-6D13-4A2B-AE89-08A030DA4402} - C:\Program Files\pdfforge Toolbar\WidgiToolbarIE.dll
- O4 - HKLM\..\Run: [SearchSettings] C:\Program Files\pdfforge Toolbar\SearchSettings.exe

(3) Unsure
This one is part of Dell but in case you do not own a Dell PC/laptop then, please upload DKabcoms.exe to VirusTotal